Reading between the lines... The problem is that the flag was not his flag. Some Mexican students had put this flag up to show support for illegal immigrants. The American students took it down and burned it.
If they'd burned their own Mexican flag, it wouldn't have been an issue.
It wasn't just "some American students" it was ROTC members who were in charge of the flagpole. The first time they put it up, the ROTC took it down and returned it to them.
Then they put it up again.
After that, the flag was retrieved again by the ROTC and disposed of.