Actually it's not that unusual at all. Many parents support their children through college. My Dad did. He supported all three of his children through college. And, often iit is part of the divorce settlement.
Well if he is indeed sending "you" money on your "grown" son's behalf for his tuition, then that admirable. I don't know you and I'm not calling bs but I'm not not calling it bs at the same time.
Have a nice day.