You're being obtuse. Assuming GP is stating the truth and it happened in a school's parking lot in the middle of the night, then the entire location is incidental and not meaningful in the least.
It's simply not helpful to group them with the shootings that happen during school hours and target students/staff.
No, not really. Think about it: who is somehow trying to argue away school shootings based on arbitrary assertions? Do you think you can argue away the gun violence out of school grounds?
I would dare say that gun violence is bad all around, but here we are, trying to argue that some episodes should not count because of reasons. That would certainly reassure those attending those schools, as well as their family and communities.
Arguing that gun violence is bad all round is fine. But this isn't that? It's exploiting the special emotive value of the term "school shooting" - something that will obviously be read to refer to a specific kind of circumstance that everyone understands - in an attempt to colour as many possible instances of gun violence with the seriousness with which the authors think they should be regarded. Or so it seems to me.
It's not that it's less serious, it's that it comes from a different circumstance and affects demographics that many gun control advocates don't actually have any interest in helping.
That could be motivation if one doesn't mind absurdity, like “gun control yes, but you're exempt if you pinky-promise you only shoot <people-I-don't-like>”.
It's simply not helpful to group them with the shootings that happen during school hours and target students/staff.