What they don't tell you is that there was a FREE concert after the speech.
Actually, the concert came before the rally.So, anyone who came solely for the concert presumably would have left. Or at least been holding up a sign in support of the band.
By the way the band was a group called The Decemberists. That's right, those The Decemberists. You are probably familiar with their long string of radio hits and their sold out stadium world tours, so I will not bother dwelling on their popularity for a second longer.