Yes, I'm trying to be a little funny but the point is that (outside perhaps work?), you should probably be a bit more engaged with the people that mean something to you.
My girlfriend has autism and when I want her attention I need to ask for it like 5 times over a space of 20 seconds, if I don't ask multiple times she will literally forget I even asked in the first place. Sometimes it literally takes a minute. This isn't because she doesn't care about me, it's just how her brain works.
Maybe this is just a better form of communication for him while he's focused on work. Please don't assume ill-intent, it just seems unnecessarily rude.
I know multiple people who need some time to switch to you when they are focused (either they can't listen before, or they can but would lose their track). And that's fine. And they are probably not autistic. They usually don't need to be called multiple times though, that would be a bit annoying but hey, what can one do. I'd probably get used to it.
I don't usually need time to switch to someone interrupting me but certainly don't like it when the other one assumes I'm listening before I showed I'm listening.
Anyway, if any of my friends would be offended by being ignored for some hours, they're going to have bad time in our group.
If someone is neurotypical and fully functional... maybe? For someone who isn't, this is basically "try harder to be normal", with all of the guilt and judgement that implies.
For example: Telling a person with chronic clinical depression they have no reason to be depressed and are being ungrateful for having a successful career.