We now know that he was picked up on warrants for graffiti. Thom Garvey at the Hub Review has some thoughts about the incident, along with some relevant links.
But I did laugh this morning when a commenter on the early Boston Herald story said:
"I hope he was arrested on charges of attempting to dj his own art opening. I hate it when people do that."
I can't find the original story and comment, but I'm pretty sure I got it right.