As usual, you're missing some essential thing. The Telegram channel used to coordinate terrorists is controlled by Ilya Ponomarev. So it was indeed organized from Ukraine.

Reaction of officials could be faster, but we've seen arrests and we'll see trials.

USA always expressed support for "anti-Russian rebels" on Caucasus, even for Chechen bandits and slavers.

So in general it was a riot coordinated by your friends and performed by your friends.