I didn't teach him that

We have been working with Cooper on not hitting. Sometimes he hits, and sometimes he just gets overly enthusiastic in expressing himself. When he is hitting, we say, "Only happy hands!" When he gets carried away I remind him that he needs to do gentle touches. We were playing today, and he started poking me in the face. I reminded him, "Only gentle touches." So he started holding his finger half an inch from my face and laughing. He doesn't actually say, "I'm not touching you," but I can hear him thinking it.

Where do they learn these things?