Saint-Supéry signed with Valencia in Spain, which was where Sergio De Larrea was playing. (25th pick in the draft) They gave him a bunch of the money freed up from De Larrea's contract.
I think a lot of us underestimate how difficult it can be to move overseas at such a young age. He gets to be in his home country, up the coast from his hometown, and still make a bunch of money. As De Larrea illustrated, if you play well, you can still get drafted. Liga ACB, where he will be playing, is widely regarded as the best domestic basketball league outside the NBA.
Gonzaga also lost another one of it's starting guards Jack Kayil, to the draft. (#39 pick->Knicks) Many were expecting him to return in early projections, so the backcourt there is a huge question mark.