People get bored.
All it takes is one guy saying to himself 'this'll be funny' and that's that.
They don't have to care.
Of course, we
care, but honestly I don't think it was motivated by anything. If it was or wasn't, it doesn't change how things are.
If there's a way to fix it, great. All the spam happened at the same time so a rollback should get rid of it. If there isn't... well, we'll just have to move on and carry on.
Risks are taken when you host something like that on a platform that's open to this kind of thing.