Is it possible your son was molested or abused?
This is, to me, outside the realm of what is normal.
DO NOT leave him unsupervised with other children... what if those kids goes home and tells their parents what your son did... and what 'games' they played while at your home???? THIS is a problem... and they would have every right... to keep their kids away from your son, too. OR to heavily question you about it and WHY they were unsupervised doing this in your home, in his room, in his bedroom etc.
AND what if he acts out this way... at other people's homes???
GOOD you are taking him to a child Psychologist.
Next: who is your son around... besides you? Who else, takes care of him, who else does he spend time with etc.?
all the best,
Susan