My son, 7 years, after going to park, cinema or anything else at the request "Did you enjoy" answers "no" Why?

He seems to enjoy staying with others, running, playing and so on but he doesn't want to give us satisfaction about it...and when my wife gets mad about his attitude he replays he is joking. How can we change this attitude and why he try to act like we don't exist just after we come home? Tks. (Sorry for my mistakes, I am not american!)