Somebody logged into his bitcointalk account after he died, so he gave someone else the password to it. It's possible he also gave someone the password to his wallet.
Maybe he didn't give anyone his password and they just booted up his computer. If bitcointalk was one of his open tabs or homepage that could explain it.
On top of that he knew he was terminally ill for a while, so it's not like it's hard to believe that there may be a chance he gave his family his wallet password.
Where did I say that? (though it is more likely).
If he was terminally ill why wouldn't he have made arrangements to return the money? Has his death actually been 100% confirmed?