lol...dude move the fuck out of the house. Okay to be fair, I've got close friends in India who I know live with their families their entire lives as part of their culture/religion...and this is actually something they like to do as well (As an American, this is very hard for most of us to understand, as growing up and becoming adult and moving out of the house is all kids want as they grow up..that's what we look forward to) and maybe this is the case with your friend? If so, if he chooses to live with them as an adult because of cultural reasons..than I would say be honest. I'd also say sorry but I'm a damn adult, I can bet if I want to.
Sounds like he's got enough money to leave the house now if he wants.
Well, it's obviously not an option for them to simply say that he is an adult and he can do whatever he wants because if the parents are strict, that will simply make a big issue between him and his parents, they might kick him out of the house and cut the strings off and tell him to never see them again. He might get free from one thing but it is not really a good thing to make your parents get mad at you so badly that they ask you to never face them again.
That is probably the reason why he is feeling that way and is afraid to discuss it with his parents, but if I was in place of him, I would probably just let them know that I've won a significantly high amount and would ask their opinion politely as to what should be done with it, if they are religious and strict, they would probably ask him to never use it nor bring it home or something.