Wait a sec. How is he eligible, then?
Young players on these professional clubs typically aren't given anything more than room and board to remain with the team. They're essentially just youth team trainees. There is no high school basketball to speak of in Europe.
The Enes Kanter situation occurred because he was so gifted at such a young age he essentially became a full senior professional. (That case was kind of a mess, Kanter had explicitly turned down lucrative European offers in order to remain college eligible, but that's the NCAA for you. Let it not be said that Kentucky gets everything decided in their favor)
This is all grossly hypocritical of course. Giorgi was probably "paid" more money for his services as a basketball player than most of the kids who are made into cartoon villains by the media in the US. But because this is the only route in Europe for players of any quality, treating living stipends for youth players as an NCAA violation would essentially ban Europeans from college basketball, which isn't an outcome that anyone wants. The NCAA is perfectly capable of being practical when it wants to/has to.