If he/she/it is on a public street/sidewalk, they do have the right to film “wherever and whenever they please.” There is no indication that they were trespassing onto private property. It is not illegal to film something in plain view from a public street.
Even youtube freakazoids have inherent rights to speech and press. School security should have stayed on campus. In this case, it appears that guard overstepped their bounds.
I don’t disagree but you would think given the climate they would ask or let them know