I’ve seen LMB fry ball up and tickle the surface like that
Would there be thousands of them in a school? I'd estimate there were at least 10K between the 2 schools.
It would be cool if they were LMB as my pond could use some more bass. I'm leaning more towards them being GS fry as I think they probably only hatched today and would still be guarded if they were bass fry. I belive GS eggs are simply laid on grass and hatch unattended.