First, that the pranksters were so egregiously responsible in the way they went about it. They avoided disrupting any actual educational activities; it was meant to be harmless fun, not vandalism. No harm came to anything here.
Second, that they documented their findings to the administration as part of the action, including recommendations for improvements.
Third, the administration took this as exactly that: a harmless prank by smart, ethical kids who ALSO did them a favor by pointing out the vulnerabilities. If the admin had a panicked fit about this, they could have made it an ugly situation.
My educational experience was populated far more by "freak out and yell" types than this school district, which was a shame.
In our high school they didn't expose the gradebook in that you could get in and change it, but we were able to see everyone else's grades. Teachers would post grades for their class and "obscure" it by posting it with the student ID (you were only supposed to know your own) next to the grade. But when the posted, the entire list was still in alphabetical order so it wasn't hard to figure out everyone's grade and student ID.
And the cherry on top of this was that all the students' passwords were their student ID.