It's not a great start, but I think you also have to leave some room for a kid just needing a little growing up. The Celtics can give him structure. Get him a driver to practices/ games. Brown and Tatum can make friends and teach him new habits.
There's some risk when a kid lacks work ethic, but if he's not out of shape, not committing crimes, not clashing with teammates, not having substance abuse issues, etc... it's also too soon to judge how he'll react to the NBA life.