It doesn’t seem like George is in the caves. I am not sure where that location is at, but it seems to have walls and doors. I think George is just wandering around, though he could have been released by the Evil Queen or Hyde or Gideon or the Black Fairy. There is a lot of ways he could be loose.
I do think that we are possibly seeing more depth then there is here. It definitely could be anyone because these writers write the most random nonsensical things to happen, but i really think this time it is probably just George via Hook.
The Murder Most Foul might have to do with the visiting of Charming’s father’s ghost. Maybe he gives information to them. Or just all the murder revenge in one big family, especially if Charming kills George. Hamlet’s father is killed by his uncle who marries Hamlet’s mother. Hamlet then kills his uncle and love and mother, sort of, and various others. I wonder if they will say good night, sweet prince? Do we know what Charming’s father’s name is? I can’t remember.