It’s an interesting question, to be sure. But it’s a rather unusual focus in the larger context.
Perhaps let’s take a different angle on this. Instead of male high school kids waiting for a bus, let’s say it was a girl’s high school cheerleading team in cheer outfits waiting for the bus. And instead of Black Israelites yelling racist and homophobic slurs, let’s say it is a group of frat boys cat calling and making vulgar sexual comments. What would happen if one were to raise the question as to why the girls felt it appropriate to be wearing revealing clothing in front of sex-starved college males? What kind of chaperone would leave a bunch of “scantily clad” girls in front college males who would get worked up by it? Now, yes, why a chaperone would do that may indeed show poor judgement, but do you think that would be the appropriate direction to look at that situation? Is that a fair assessment — at all — of the situation, that this is really just a chaperone problem? Would that question be able to make it past the “OMG victim blaming” filter? Do the frat boys get the pass because “it’s just what they do” and all blame lies on the feet of the chaperones and the girls for “dressing scantily”?
Does the chaperone tell the high school girls that it's OK to start yelling at grown men in response? Plus, I think the conflation of wearing political messages (actual speech) and scanty clothing (not speech) harms your comparison instead of aiding it.
It's not just a chaperone problem, but that's no reason to not fault the chaperone as well.