Maybe burning a personally owned flag could be what the jurists defined as first amendment protected speech, but I believe the flag in question flew at the school, owned by the school and the patriotic students took umbrage, tore it down and burned it. Absolutely no coverage by the supreme court ruling IMO and Trumps suggestion to yank citizenship for these morons (if they even are citizens) could be useful in ridding us of vermin of that caliber.
If that is the case, then burning the US flag per se isn’t the issue . It is taking someone’s property and destroying it with fire in a protest. Take out US Flag part of the equation and insert any other sort of flag to look at the legality.
That said, I love when Donald Trump Trolls people. He is The World’s Greatest Troll
https://www.youtube.com/watch?v=fzkBfTfiXS0