I can see him knowing about the crystal ball from the movie but then he would also know about the flying monkey. My point is that he knew instinctively that his father had the crystal ball from OZ. How did he know this. He flew to his castle to find it. So, if he wasn’t surprised to find the crystal ball from Oz, why would he be surprised to see flying monkeys, especially if he had seen them in the movie.
But he didn’t know that his father had the ball. He knew that his father had backup plans and most likely there was something in that castle that would help him. It was when he opened the door and saw the ball that the light went off–“oh a crystal ball! I can use that to see people”
As for the monkeys, I actually think this adds to the point that he hasn’t been to Oz. He was surprised to see them–thinking them only fictional. Ruby slippers and crystal balls are one thing but Neal has experience with portals (extensive knowledge in fact lol) and knows that crystal balls exist in general but flying monkeys are something that are almost too fantastical. Even Snow White doesn’t know about them.