Well, then, we will agree to disagree.
Kids often think stupid stuff is cool until on of them get hurt and then they say, "but I didn't do it on purpose". It matters little here if they are beginners or have a couple of years of sailing under their belts.
The person who should be observing a proper distance is the dude on the Moth. The Opti youth appear to be in a cohesive formation and this yokel is blasting along on their flank.
There's virtually no room for error here and it is dumb in the kindest of terms. If an accident were to happen what do you think would be the result... that the parents of these kids would have nothing to say, nor would they mount a suit to gain some determination of just who was being stupid?
Yes, you already know the answer to that one.
I've seen much worse outcomes from far more benign scenarios.
I will always err on the side of kids. I won't feel sorry for that position. There may come a day when you are grateful someone else did that on behalf of your own.