Testing is right. That is actually his true form. The ROTS novelization describes it as the “face of Darth Sidious” or something. He decides at that moment that it could be advantageous to keep it that way since it would appear that he was injured by the Jedi.

As for the clones, it’s correct that Rey’s dad is a completely different thing than those clones in the vat in canon (strandcast). However, even without the whole strandcast thingy (which I don’t care for myself) one could rationalize him as an unmodified clone, similar to Boba Fett.