Offer to help a clearly distressed passenger.
You can hear people around trying to calm the child down 'It's ok honey, your mum is there'. There probably wasn't a lot more that they could really do if the airline staff weren't able to get the child sitting down.
Offers of help generally come when the behaviour of the other person (or in this case, the mother) warrant it. If mum had been desperately trying to get her child to calm down or had explained the situation to surrounding passengers, she probably would have had a more sympathetic audience, than if she were sitting there with her earbuds in and the occasional 'calm down'. That's just human nature - people are more likely to help those who are trying to help themselves. Which way it was we will never know as all we see is what this person has chosen to film and present to the world.
I don't think he was wrong to film it if his purpose was to send a factual video (without the emotive language) to the airline and ask for some compensation or to ask what they are planning to do to assist passengers in distress in the future. He absolutely was wrong to put it on the internet. We've seen many cases of people harming themselves after being publicly shamed, and if this mother was already teetering on the edge, her child being called demonic and criticising her parenting may indeed be the last straw.
It's a shame that airlines can't install some form of sensory room on their planes, I'm sure that even passengers without a disability would find it beneficial, but I don't see them sacrificing profits in order to do so any time soon. I do think it's clear that being on a flight is not a safe or secure environment for this particular child, and I think that the impact of his behaviour on the other passengers and crew, regardless of the reason for it, should not be minimised.