If you watch the video you can tell he wasn't joking, but also that it's not something that he had given any thought. At all. People are calling it him "musing"... I believe its what my ol' gran would have called "opening his mouth and letting his belly rumble".
Either way its not really what the Potus should be doing but
surely we're not surprised by now. That's what I don't get (or like) - people feigning shock
.