OK so as for me.
I don't think DS' laughter in this case was misplaced emotion. It was after the whole incident and he was not laughing at me or trying to get me to join in if that makes sense, in fact, it probably wasn't even laughing - just silly noises etc. Either way some small clue that he was slipping back into the hyperactive behaviour - I have got really, really finely attuned to these clues.
It wasn't about bedtime, or at least, there are no general/ongoing issues with bedtime. This is a thing he does sometimes but other times is really good. We already have an incentive for bedtime in that if he gets ready in time he can watch TV on the laptop or play games on the tablet. Luckily screens don't affect his ability to sleep and they have always calmed him down.
The silliness - is just irritating because it is so extreme and he has no concept of when to stop. Also I think I get more irritated just around bedtime, because it's a time of day when I'm often tired and hungry (but can't start my dinner because I have to sort DS out) and also because sometimes I'm looking forward to something that I can start as soon as he's in bed and I want him to hurry up and go there
I'm often trying to do something on my computer and don't have a lot of patience for listening to jokes or whatever. He also tends to watch annoying youtube videos over dinner (yeah, we have shitty habits of feeding him separately and he watches TV, mainly because he seems to find it literally impossible to sit on a chair and DH and I end up chewing our own hands off trying to avoid reacting to it, or we bitch at him constantly for the entire meal and it's just miserable. Plus it's too early for us to eat but not want to snack on junk again later.) So Family Dinner happens once a week, and the rest of the time he eats in front of the TV and falls off the chair approximately three times a meal. Dinner is sometimes late, so he just carries on watching youtube until bedtime. If it's earlier then he will go off and do other things and if I have energy then I am going around doing various things.
But when I don't have energy AND dinner was late (because I had no energy) AND he's been on a youtube spiral AND I'm rooting for that bedtime and plugged into my screen, that triggers it. So I think it probably is an attention thing. Whereas I'm thinking "Oh thank god I got through, almost time for no attention needed, yay!" he is thinking "But I didn't tell you 500 unfunny jokes today. Or ask you baffling science and geography and history questions! Or do my impression of a toaster. And we didn't play a game. Time to play a game!" and trying to squeeze in that last drop.
In fact, it's better recently because he doesn't always have tickets by that time of day so he doesn't always watch TV in a constant line for hours, which is a bad habit I let him get into when I'm tired or overwhelmed. When he's not watching TV he is more likely to interact with me in a way I find acceptable, and when I'm not plugged into my screen I am more likely to respond to even his annoying behaviour better.
I'm now 99% sure that I have AD(H)D, so it would not surprise me if DS had it too. But it's not really relevant for now and will only really become an issue if it bleeds into school, at which point we will start the ball rolling, or they will. So whether this kind of frustrating behaviour is my fault, a quirk that he will grow out of or a genuine difficulty is sort of unknown for now.