"Are college coaches/recruiters looking for potential recruits at these events, or do they already have an idea of players they like and are only there to watch them?"
It's not an either/or situation. Both things go on.
The smart path is to engage in concerted communications to try to get your target schools to take an interest in you.
But if you stand out on the field, people are going to notice.
I think if you are trying to divine the ultra best from the very best, the way a pro scout has to in preparation for the draft, it takes a lot of experience and training to have that level of discernment. But to see just who's the best in your average high school game, really you don't have to be all that highly trained. Quite often the top talent kid will jump out at you in all sorts of ways. Anyone (other than those blinded by a terrific bias in favor of their own kid) can see it.
Things are going to be different at a WWBA or comparable event, because when you're out there with every player being a potential collegiate level player (or better), if you're hoping just to stand out, it's a tall order.