I already gave you some ideas on how to deal with the situation. But you brushed them off as too much work.
There are a whole group of us that to the outside world look as if we are just like everyone else. That's why it's a hidden disability. Some are happy to embrace this fact (like me) and tell people, others less happy (like a PP).
Most of us struggle.in social situations, we don't understand the constructs that the majority do. We think literally rather than abstract. If you ask a question then we answer it, we don't think to elaborate (unless the question specifically asks for this), or ask questions back. We might take longer to answer as we try and work out what is the most socially appropriate answer is. We may not realise that it's our turn to talk. We may not always translate what you've actually said correctly, remember we think literally, we don't generally say one.thing and mean another. We don't do small talk.
Many of us also have sensory processing issues, and in the Brunch situation there will not only be people we don't know, but also the noise of everyone chatting, the smell and look of foods that are unfamiliar, maybe a light fitting that's buzzing (yes many.of us can hear electricity) or a clock ticking. We might struggle to concentrate on the single voice directed at us, to the point that we are only capable of the single word answers. It may be all we can do not.to.turn around and run out of the venue.
Now I'm not saying that the person in your encounter was autistic, but if he was this is just a little of what he might have.been experiencing. And yet he still thought enough of his friend to turn up to an event where he knew things would be difficult.
Contrary to what you think, not everyone is capable of the level of social interaction.you seem to think.is obligatory to go to a social event. But that doesn't mean we should be written off.and forced to stay at home. We are just as deserving of attending, especially if we were personally invited by the host (who probably does know.how hard it is for us to even walk in and appreciates that we have made that effort).
All we ask is to be allowed to mingle at a level we feel comfortable with. And tbh this is how you should treat everybody, ND or not.