I know that if I was a Palestine protestor, and President Biden was going to speak, and the college said that they would immediately just end the ceremony if things got too out of hand, I would immediately think "Well that definitely wouldn't be a good outcome. I better quiet down; I was going to have this big protest, but if it'll end the commencement ceremony entirely, then I won't, because that would attract some attention to the cause I'm trying to promote. It might make the news or something. I'm scared of that outcome and wouldn't want it to happen; that threat is effective."
Your conclusion makes perfect sense that the crowd was mostly filled with people who were seething with contempt for Joe Biden, but cowed into obedient sitting-facing-towards-him by the threat that if they made too much ruckus, it would successfully disrupt the event.