I have name changed for this. I have autism. I'm not at all sure I'm going to be able to explain this helpfully, but I wanted to give my take on it anyway. I'm trying to understand and offer thoughts, not argue.
Autism is not something people can help having. I imagine your sibling has found things very difficult through life and I guess that might bring extra problems and issues like anger for them. I know neurotypical (nt) people have difficult things too. I do think the world is set up for nt people at the moment, probably understandably, but I hope and think there's becoming more understanding of differences.
I'm not surprised you felt hurt when you were cut off with no explanation, it must have felt baffling and cruel.
From what I understand, this can happen with autistic people, as Loubelle said, and I think it is different from the 'going no contact' thing we often read about where, for example, someone has to stop contact with an abusive relative, which is sometimes the right thing to do. In those cases, those people often say they feel relief, lighter, and much happier for stopping contact.
However, I've stopped contacting people I love, because I just couldn't deal with the pressure, interactions, layers of issues that had built up and that I felt unable to unpack or articulate. I've hated myself for it and missed them and felt miserable. Someone else would probably have been able to speak clearly and directly, have a bit or a row or a laugh at something, but I've felt overwhelming stress and inability to do this. I think that might be part of the autism. It might be they hate the struggle of being themself, not that they hate you.
However, I can totally understand your dread at future interactions and I'd understand you not wanting anything to do with him.
Please don't think of your sibling as a 'random employee' though, I think that's cruel. I read somewhere that it's not a problem with interactions autistic people have, it's a problem with inauthentic interactions. If you think of them as a random employee and then treat them as such I think that would make matters worse. (Also, I'd hope all employees would be treated well anyway, not dismissively.)
No idea if any of this makes sense, but good luck with it all.