He grabbed 1.4 rebound his soph year in 22min. now hes a sr with 26mpg. If anything, I would say his JR year is the abberation. Something like .8, 1.4, 1.7, 2.0, reb/game looks much more in line.
Without looking at your team history, my thoughts were his SR year, you had the best team and forced alot of missed shots, which explains the 1.4 def reb/game, while last season, your team was much worse, explaining the 0.6 def reb/game. The .3 oreb/game increase is probably because he is better this year than yrs past + some random noise.
And after checking out ur team, my theory seems to fit.