Staying on the ground after getting knocked down with a big move is rather common. People take time to compose themselves; that doesn't mean they're defeated or knocked out. That's what happened back in EL, and this attack is a call back to EL where Lucci wasn't actually KO'ed.
Even Saturn, with all the regeneration in the world, took long enough for Kuma and Boney to have a reunion before he came back to attack them.