He was really, really good at Summer League. Co-MVP for Vegas, I believe.
You are correct
"Selby, the Grizzlies’ second-year guard out of Kansas, led all players in scoring at 27.5 points per game as Memphis went 2-2 entering its final game Sunday. Selby shot 59.3 percent from the floor — including 70.6 percent on 3-pointers. Selby made at least five 3-pointers in each game, talling 24 in the four games (24-for-34). Selby was also active defensively, averaging 2.5 steals."
http://hangtime.blogs.nba.com/category/2012/2012-summer-league/
Yay. I was surprised he didn't get to play more but oh well.
Here's a partial explanation from David Thorpe, regarding his lack of good play during his college days. But this could speak to his not-so-great transition to the pros as well.
"Selby is being asked to play within a defined system, and he's completely lost in that environment. His DNA says "go go go," but his system requires establishing paint dominance with the Kansas bigs, then reading the defense and delivering the ball to the best positioned teammate. Without doubt, this new way of playing is causing him all sorts of problems, mostly taking him out of his comfort zone. He's thinking instead of playing."
But maybe there is some hope for young Josh.
"But now I'll remind you of two other players who were not great, or even very good, in college: Jrue Holiday and Russell Westbrook. Both played in a similar system at UCLA, if only at a slower pace than Kansas' running attack."
http://www.kcsr.org/showthread.php?t=86300