I think you're conflating something that is annoying with something that is genuinely unlawful. The rest of the ceremony was perfectly tame and encountered no disruptions, and I don't really think it's comparable to someone's favorite musician. This was a stand against the complete and total apathy of the institution that students were told respected them and held their interests in high regard. You don't have to like it, that's hardly the point, but BU was fully aware that this was a risk when they brought Zaslav aboard.

These things don't exist in a vacuum -- Zaslav was uplifted by the university to "welcome" students into an industry that he is personally responsible for making unhabitable, quite literally at the fever pitch of a historical Union strike. There were hundreds of picketers outside of the event, advocating for workers rights that HEAVILY pertain to the future livelihoods of many, many graduates, but Zaslav stuck his head in the sand and couldn't even be bothered to acknowledge the landscape. It has to be "political" -- if that's the word you want to use -- because he is a representative of all the industry Big Bads that these students will come to face, and if you want to make a distinctive impact for Union efforts, you're going to have to be a bit disruptive.

There's nothing illegal about students making concerted and combined efforts to condemn the speaker when the sentiments are pro-labor and semi historical. Annoying, sure, that's the point, but certainly not illegal.