He had a tough decision to make. IF everything was equal basketball-wise, then choosing Duke over UK, from a school standpoint, is arguably a good choice.
However, basketball-wise, things are not exactly equal. Both programs are at the top. But teams needs and rosters are different. He chose the option with more depth at his position. That must mean he is confident he is good enough to get enough playing time to show the NBA what he can do.
It's just possible, however, that his confidence is greater than his skills and he ends up spending much more time on the bench at Duke than he would have at UK. Time will tell.