I don't think he's a Groyper.
I think he was immersed in a world which most of us don't understand and don't recognise.
There's a decent chance he was taking the piss, even he was knowingly posing as a Groyper. Remember he dressed as Trump for Halloween.
The whole shtick of 4chan is to take the piss and do things for the lols. It can be overly serious but the flip is this ironic out of bounds humour that touches on things that can't be said out loud in the real world. It is very much about pushing boundaries and being as offensive as possible to anyone and everyone. It hates authority. Within it you have almost gangs and gang like behaviour. Sometimes people egg others on and sometimes you get these enormous fallouts because there are these weird codes of conduct of how you should and shouldn't behave. Anything goes except it doesn't. It's difficult to describe really except it's the wild west and therefore probably feels a bit edgy and dangerous to kids who live in a rigid world of straight behaviour where your whole life is mapped out at birth. It's people (over whelming male) who perhaps want to escape these expectations and don't conform who are probably most drawn to it.
So the above comment about expecting people who grew up when Michael Jackson was black and Elton John was straight doesn't even begin to get close to the issue.
Even young people often struggle to understand it. Trolling died something of a death over the course of the last ten years as cancel culture kicked in. Those of us who were early internet adopters and understood the wild west aspects and were onboard before internet search safety features were bought in, perhaps understand it better than may kids today who are just on the reaching end of abuse rather than understanding trolling. The way the internet has developed and you can block means you are protected from it to a degree that wasn't there before. You have to go off hunting for those communities whereas in the early days of the web, that was a huge part of the online world. This has survived mainly in gaming and through 4chan when it died off elsewhere.
So I don't think it's necessarily an age thing - there are people in their mid to late fourties like DH who would have an understanding but perhaps not be up to date with the latest shite and young people who are in their early twenties for whom this is a totally alien world. It's a mindset separate from the real world. It's niche and it's usually a world for outsiders and the disaffected. Which is why this element of anti-establishment is a reoccurring theme. There's a sense of hopelessness and frustration and an inability to raise certain subjects because they are taboo or off limits in society way which leads to these subjects becoming twisted and festering underground rather than being dealt with in the open (which ironically Kirk was right on). We perhaps understand coming from Incels as it's better known but I think this is potentially slightly different. It's an anger at the world not serving 'people like me' still. So anyone in establishment full stop - unless they've been through gaming or were part of this early online world won't have a clue how to deal with any of this even if they are young.
Curiously this guy from what's out there looks like he has probably engaged with extreme right wing stuff on some level even if he has rejected it. It's someone who has been exposed to a wider range of beliefs than it appears to someone who doesn't understand internet culture.
And then there's the elephant in the room; all shooters are the product of the failure of their own communities for some reason. And he was a product of a middle class conservative right wing gun loving Christian republican supporting family. And there's the problem of where do you go from that if you rebel? The governor's comment that he 'prayed it wasn't one of us' and that his prayers were not answered was a telling one. They know the issue is about a failure within their own community rather than it being a pure radicalisation issue. They know it's a disaffection issue but won't be willing to admit that. Looking inward is harder than looking outward. It would have been easier for the Christian Right to accept if it had been 'an outsider', and that's part of the point.
There's also the factor that he appears to have reacted in a way that you'd expect from someone with a gun touting right wing background would react if they felt betrayed by leadership from the right...
Has this come from university lecturers who again are part of the establishment? No this is online culture. This is gaming culture. This is again problematic for the Christian right because large parts of this world are heavily right wing and have issues that the Christian Right won't want to deal with because they support their way of life.
So yes I think we will see a back lash against 'left wing universities' because it's an easy out to deal with this scenario. Equally the left will put their hands on their ears and disavow this guy as not one of their own.
My final point which is noteworthy is that on of the features of radicalisation is this purity spiralling and need to 'prove' your values. There is a pattern of individuals who come from 'the outside' taking on behaviour which is more extreme than those who come from a background where those values were more typical. Thus you get converts to religion being more at risk to radicalisation because they feel extra pressure to prove they belong.
This shooting would therefore fit with patterns of radicalisation akin to religion, it would fit with a right wing gun culture, it would fit with youth disaffection with mainstream politics, it would fit with difficult online communities which are out of sight from authorities, it would fit with the lone, quiet gunman AND it would fit with uncontrolled and unchallenged purity spirals within left wing politics.
But I doubt you'll see many people reflect on all these patterns, instead they'll focus on whichever element best fits their agenda.
I think we have a perfect storm scenario that's only growing. I suspect we will see others from other areas as youth disaffection grows and anger at the establishment rises. Historical data shows revolutions and civil unrest is much more common with high youth unemployment / underemployment and declining standards of living regardless of political affiliation. It's important we look at this from all angles.