Not that he did anything illegal, but he may have been a danger to other cyclists, pedestrians, joggers if he did have some mental illness. Not moving when he knows someone is behind him and then wacking me in the face when I pass is rather aggressive and could have been more violent depending on his mood.
I wasn’t about to stop and have a chat to determine that and would have simply alerted police that there is someone on the bridge who may be aggressively violent.
Maybe he was just one pissed off dude—either way, it was not a good situation.