And I agree, there is no problem teaching her what she did was wrong.
Again...messing with a peer on the toilet IS weird because you (as an adult) associate that as being weird because of what you know. As a kid, they ALL go to the bathroom (boys and girls), they are equals. They may not associate that as being weird because they don't understand...which is why you're right, it is a good time to teach privacy. But I wouldn't look at the child's behavior as a red flag or weird.
She probably didn't even think about it because she didn't KNOW she should.
This! So totally this! Especially the part I bolded.
Kids do silly things because their innocence lets them. They don't think of it as wrong because they have no comprehension of anything sexual, so it's just someone having a poop, and at five, poop is funny.
There was a strange situation at my son's school this year. He's also five. The art class is in a seperate building, and there's no bathroom. My son had to go, the art teacher hates letting them go because she's by herself, and the kid would have to leave one building and go into the next building (it's like 10 feet away is all) to get to the bathroom.
But he was doing "the dance" so she had to let him go. My son goes outside, notices that he's by himself, and he
really has to go, so instead of going into the building, he whips it out and pees on a bush.
The teacher was inside, but keeping an eye on him, so she saw what he did. She said she found it very funny, but also knew it wasn't "allowed" behavior, so she asked me very nicely if I could kinda talk to him and explain that he shouldn't do that anymore.
So I talked to him, telling him that some things are private and basically that no one wanted to see his boy bits and you never know who's watching from a window.
From that day on, my son will not let anyone see anything. Not even mommy. When he changes his clothes, he goes into the bathroom and shuts the door.
So while I understand the importance of making sure they know about privacy and appropriate behavior, it's still a little sad to see some of his innocence stripped away.