They record what can generally be seen. However, I also see magic that is invisible to most people. If some magic has a consequence or casts light or sound, the security cameras would pick it up. But if some magic phenomenon, spell, etc happens that is not usually seen (say, teleportation that simply makes someone be somewhere else) your cameras would see the person appearing, I could see the magic also making them appear. And with this magic that shows not what people remember or saw but what happened, it shows me that magic as well.