They have no intention of voting for him--they thought it would be a fun experience, and they had a restaurant in mind as well.
I've gone to rallies of people I'd be unlikely to vote for, too.
If Trump was speaking nearby, I'd bring a camera and try for a good spot--doesn't mean I think he's anything but a massive ass, though.
That said, Bernie says some positive things. He will not get my primary vote, but I don't think he is a 'bad' guy and he does seem to care about the working stiffs. My major disconnect with him is that he has no ability--and hasn't indicated any clue--as to how he will persuade a Congress, where he worked as an independent, caucusing with the Democrats but NOT doing any of the gritty administrative legwork expected of most in the caucus--to do his bidding, should he become POTUS.
I just wonder how well he can "work a crowd" when that crowd consists of legislators with their own agendas. It's not like he's ever whipped votes, made trades, cut deals, or done any of the vote counting work in the Democratic caucus, because he's not one of them, he's never held a peer position in the House or Senate party structure--he only has sworn to vote with them on procedural matters, not on legislation. He's not part of the "Party Discipline" set (and they can muster that discipline if it means enough) in that regard.
I honestly don't think he has the political persuasive chops for that kind of effort--he'd need a wingman who knew the Hill really well (it's why Cheney made Bush pick him).