Since the only enemy besides the guards was apparently a single plane, I'd say Russian intelligence didn't get a whiff of this attack and didn't have more planes or ships in position.

So Russian intelligence failed to see this attack, Ukrainian command managed to keep it under wrap and still bring enough forces to see this through and the operation was swift enough that the Russians couldn't reorganize.

Ukraine picked a battle it could win and did. Not much more to ask for, just well planned, well done.

Similiar to how at the start of the war there were many battles Ukraine couldn't win - so they didn't fight them in the first place. That's strategy.