That is right, one FULL push-up with a clap.
Surprise is completely natural. I was a little shocked too, at the realization that I have never done this before. With hundreds of thousands of regular push-ups under my belt, you would think this would be a no-brainer. I found it surprisingly difficult though, for some reason.
At last, after five or more tries, I finally succeeded in clapping my hands together without banging my face into the floor.