Police Lives Matter is a racist response to Black Lives Matter, the same as Straight Pride protests Gay Pride.
What we saw here was two conservative kids in politically charged kit looking to provoke a scene in a "multicultural" zone, and a liberal activist took the bait.
Just to be clear I think police lives absolutely matter and I don't think straight people are any less important than gay people, but emulating the form of one protest movement to promote the opposite is an appeal to ridicule. It's a direct attack and doesn't actually serve to support the named cohort. Police Lives Matter is an opposite to BLM because as this woman pointed out, one of the problems BLM is looking to correct is the treatment of the black community at the hands of law enforcement.
I had never actually heard of a multi-cultural zone in a school before this incident, and safe spaces didn't exist when I was college, but it seems pretty obvious the two white kids were looking to cause a scene and they got it. I like the school's reply that it's OK to create a discussion on these issues, because I agree. You and I are likely polar opposites on these issues and this confrontation has created an situation where we can talk about them.