comes over to my truck and then lays his hands on my door and starts to say something."
Fact #1: you initiated the conversation with him. He responded on precisely the same level you initiated. For that, you assaulted him.
"Just as the light changed ... I didn't try to get away, I didn't try to hide, I just drove home."
Fact #2: by your own description, traffic was not being held up by the protesters, but rather by the stop light. The protesters were engaging in their Constitutionally recognized right to peaceably assemble to petition for a redress of grievances.
That LawEnforcement has not bothered you does not mean very much. They don't enforce laws anymore, they just enforce order, be it lawful or not. And they crack down on disorder - be it lawful or not.