Then Bring out the Mace Guns and Billy Clubs and stop taking pictures.
An under cover LEO does not blow their gig to make an arrest or enforce the law unless someone's immediate safety and more so their life is in danger. If the LEO has been able to pass as a college student, I'm willing to bet that there are much bigger fish to catch on campus than a few couch killers. Such as drug dealers, thieves, rapists, etc.
You (and many others in this world) are making a lot of assumptions when you've not ever walked in the shoes of an LEO, are familiar with the laws, or know the department's SOG. It is little different than being an armchair general to soldiers in the field. Hold fast your tongue and remember that you simply do not know except what a few pictures show.