"Do you see the catastrophic thinking etc as part and parcel of the AS, or as part of a comorbid anxiety problem? "
The anxiety is part of the AS, so I'd say it's impossible to split the two.
Because our brains don't have a 'filing clerk' to stare into the filing cabinet for "things that aren't actually an emergency at all", we don't know how serious something might be. We just know it Might Be Very Scary.
And because we can often only visualise one person at a time in our brains, we can't reason that there's lots of people who can help us - we just get fixated on the problem, the rude person, the thing that isn't right. With no fast wiring connecting the bits, there's just no way to switch off the amygdala bit of the brain, so it keeps panicking.
(The amygdala is an ancient bit of the brain whose job is to spot angry faces or scary situations and decide how long to panic for. So something truly scary happens or if an angry face comes into view, we can't find out how serious it is. So... the amygdala presses the Big Red Panic Button and just keeps pressing it until someone, somewhere, gets the info across to it to say "no, it's not that serious, just calm down".)
Social stories do that. So do other visual things that show a scale of how serious it is. But it has to be accurate, or we lose confidence in the stories/symbols. If you say "oh it's fine" and it isn't, that's even scarier.
Wrapping ourselves in something very enclosing is a quick way to switch off the panic button too. Using words to calm us down is more tricky, because if our brains are using our eyes to look for the danger, they won't use our ears properly at the same time.