Kindergarten bathrooms, are icky.
At this age, they are not rocket scientists about neatness in the bathroom.
It is also the Janitor, that can be called, by the Teacher, to clean the bathroom if/when there is pee/poop all over.
This is what my kids' school does.
IF a kids' bathroom, has pee all over or on the floors etc, the Janitor can be called. Or sometimes a kid will have vomited someplace. The Janitor can be called. They don't just work at 5:00pm when school is done.
AND, TEACH YOUR CHILD... to say to the Teacher "There is pee all over the bathroom/toilet and floor..... " so that, the TEACHER, can dutifully call, the school's Janitor to clean/mop/wipe it.
I taught my kids, even when that young, to do that. And they did.
I also taught them, to use, a papertowel to handle the door handles/toilet handles.
And to put, a toilet seat cover on the toilet seat, etc. or wipe it first before sitting on it.
You ALSO have to, teach your child, about these things.
AND since you noticed, that night that there was pee all over the bathroom, then you could have given the Teacher a head's up on that. She that he/she could make sure, that the Janitor cleans it.
And yes, in Kindergarten, the kids take themselves, to the bathroom.
The Teacher doesn't walk them.