I'd just assume that any service is going to get randomly DDOSed soon after launch, even without any sort of blackmail/targeted attack. Even if you can figure out who did it, there's pretty much no chance of chasing them down.
My takeaway from this wouldn't be "this shouldn't be possible" but "this has been commonplace for decades, and will keep happening, and we should prepare for the next one".
It doesn't really matter whether it's some corrupt local agency or some script kiddie... half the world's connected, on various shitty devices, and DDOSes are gonna keep happening.