My brother is autistic and this is the type of autistic person who is hated by other autistic people. This is why autistic people hate mentioning it, because they get lumped in with these people.
Wait, this is getting even more interesting. Who is the kind of autistic person that is hated by other autistic people: (a) people that try to be nice about enforcing a no masterbation announcement rule or (b) people that announce they are going to go masterbate? Also, does your brother fall under a, b, or something else?
It's almost definitely B. Most people on the spectrum would not say "im gonna go masturbate" and those who are would use autism as an excuse for why they behave that way, which is just not valid. Autism can make it harder to behave in a way that is socially acceptable, but not like this, hence why others on the spectrum dont like people like this. They use autism as a sort of sheild to allow them to behave in ways that are just not right. The best example of this i can think of off hand is Chris-Chan, but they are an extreme case of this.
Anyways, people like this make it harder to be upfront on the fact that you are on the spectrum, because the first thing that comes to mind will be people like that.
Autistic people who announce when they're going to masturbate make all other autistic people cringe for being so incredibly unaware and making the rest of them look weird.
I don't think anyone was assuming these people were autistic. It's possible you have a skewed view because you are around an autistic person more that most people.