Prior to the draft, Gist told the Spurs he'd be willing to go to Europe if drafted. That's basically why the Spurs drafted him. He was impressive in summer league but he likely would have stayed in Austin all year anyways. So instead of having just two players developing in Austin, the Spurs could have had two in Austin and one overseas.
I think it was the right call. Not many college players willingly commit to going overseas prior to even being drafted. It basically gave the Spurs a free season to scout him and kept his D-League eligibility for two more years.
He could have won summer league MVP and I think the Spurs still make the same choice.