I appreciate everyone's responses. I was looking for feedback from people "on the spectrum" and I got it.

I want to make clear that in no way am I looking to give him my amateur "diagnosis." My only interest is in dealing with the no-boundaries behavior. And over the last several months I have taken steps to do that. Some have worked and other lines in the sand sometimes still get crossed. And I talk to him about this.

So I will keep communicating with him, both on the work we do on the job and regarding the behaviors as they arise. But yes, his manager's pop-diagnosis should be tossed out as irrelevant to fixing things at work. As far as his manager's role, it seems to be more effective at this point to keep talking with my coworker myself about these things. If disruptive behaviors increase, I will approach the manager again, just about the behaviors. At this point, however, it seems to be going in the other direction.