I need some help with this

This thing happened with another parent at Jordan's school yesterday afternoon, and it left me upset and not sure how to think about it.

There are two things. One, I wish I'd responded better yesterday, and two, I'm not sure what to do when I see this man again, which is likely.

OK.  So here's the story.

Several other parents and I pick our kids up after school and then hang out with them either on the playground or on the soccer field.  We've been doing so for months, and  we've become friends. We share snacks, we bring extra water or toys, we watch each other's kids if one parent has to go to the bathroom, etc.

The little boys in the group love love love to pee outdoors. If they can get away with it, they do.

Initially I tried sprinting over to Jordan if I saw him, but really, by then he'd be mid-pee and you cannot stop at that point.

And a couple times I've asked Jordan if he has to pee and taken him to the men's room in the school and he's come out immediately and said, "I can't go in there. It smells like poo-poo."

But usually he says he doesn't have to. And then he and one of two of his friends will take the opportunity when they are far from us.

If he can avoid the poo-poo bathroom, he does. (The bathroom back where his classroom is is not an issue.)

Usually when we are there it's pretty empty.  So if they occasionally pee behind a tree, the other parents and I are not bothered. I've told Jordan that it doesn't actually make me upset, but if other people are around, they might get upset.

Yesterday I myself had to go to the bathroom, and being a grown woman, excused myself to head inside.

When I came out and was heading down the steps, I saw my son and another little friend of his behind a tree, but basically in plain sight, pants down around their knees, about to pee. I mean, these are kids without great fine motor yet. When they pull their pants down, it's just about all the way down.

They also aren't self-conscious about it.  But they do know that they technically are not supposed to be peeing outside. They just aren't astute enough to be sneaky about it.

By this point, there were a bunch of kids playing on the field and I said, "You guys, pull your pants up! Right now! You're going to get in trouble!"

This man said, "Are those boys yours?"

I said, "Yes."

He said, "You'd better stop them right now! There are girls on the field! My daughter is one of them!"

All I could manage was, "Huh." And then I turned my attention back to the kids and getting them to pull up their shorts and come down the hill.

He was furious. He glowered at me. He glowered at the boys. He stomped past the other boy's mother. He was SO ANGRY.

He kept glaring at us for as long as we were there, which coincidentally was not long, as we'd been about to leave.  I ignored him the whole time, but out of the corner of my eye could see he was still fuming and giving us the stinkeye.

Now, here's my thing.  One, I could see if you're mad because it's in public, and you believe nobody should pee in public.

But his reason - that his daughter might, from far away, see two four-year-olds' penises? Seriously?

I kind of wish I'd said that. But then probably better I said nothing. I don't know.

But it's not a huge school, and we're on the field every day. Odds are good I will run into him. Should I say something? If so, what?