I don't really understand... What were you expecting?

It's a casino. Their only goal is to make money.
If you're a big player that means you made big wins. They want to check that those wins are legitimate before paying you out.
It would be the exact same thing in a real life casino. If you win a too high amount they will make you wait so they can analyse the pictures taken by cameras to be sure that you haven't cheated.
That's just to protect themselves from new hackers and bug exploiters that's all. Nothing unusual.