Dorset Boy
Regular
I think they already knew. Russia had the lorry drivers remember and not all the attacks were successful, so they would have known small drones were used. They won't be able to use that tactic again, so they revealed it, plus it's a PR coup over Putin who now knows that huge damage was done to his air force using simple drones.
It makes Putin look weak - the vultures may already be circling him, and this might help. If Putin goes, then a new leader might respond to a face saving operation.
Or any Putin successor might be even more hardline.