Of course it can be attributed to athleticism. Rebounding also tends to be a bit more random from game to game. I've had guards out rebound post players.
Next point, too small of a sample size.
I've read somewhere that IQ does matter in rebounding. How much of an impact it is, not really sure.
I would also add .4 to .5 rebounds to Player B's total to account for Player A's increased minutes of Player B.
Also, the 4 position seems to get more rebounds than the C position, but it could also depend on what defense you're playing as well.
But you can't really determine anything from the example above.