Three other things here that you're not factoring in, isaac:
1) You're looking at PF/C. But his SFs dominate yours in REB since you played SGs - the average difference was like 2x in REB. He avg'd 64/38 for Ath/Reb and you avg'd 59/18. And then the stats bear this out - his SFs had 7 rebs and yours had none. That almost evens up the rebounding overall by itself.
2) You're ignoing IQ which does matter. Your PF/C have: A-, B, C+, F. His are: B+, B, A-, B. His average out to a B+, yours average out to a C+.
3) Your guys were more fatigued for more of the game than his.
All in all, I think this is probably one of those things that on the surface looks weird but when you look at how it happened, it makes total sense.