If you were one of the 12-13 gms why are you passing up on him?
IMHO two reasons
a) He was very young (b. 1994)
b) he had only played in the second division of Greece.
Other than that, it is now clear he is much better than most of the guys drafted before him. But these things happen very often, especially with non-American players, check out for instance Tony Parker s, Ginobili's and Marc Gasol's draft numbers.