Call me cynical, jaded, and overly suspicious, but I think Grandpa was doing more than watching videos with the kid, and that's why the boy is acting out in an obsessive way now.
The kid replied, "Don't worry about it."
"Well, aren't you worried that your mother will come in and look at the screen and get upset?" my friend asked.
"Naah," the kid replied, "I'm more worried about her finding my porn collection."