Any game on the list linked above is counted as bundled, whether he bought it directly from a bundle, purchased it from Steam, or obtained it by trade from a tribe of little green elves at the bottom of his garden, for a pouch full of magic beans.

This IS the reason he can't join. There is no question about it.

even if he did buy these games on steam they are still bundle games

it doesn't matter where he bought it from.
if they're bundle games, they'll be counted as such.

nah every day i tried to join and one day... i can after purchasing a game (Fuel maybe)

I was told the system goes back and "kicks" them out if their account go under the $100 mark.