Questioning my call

[Beemer]

I made this call a few months back and I had forgotten about it, but I'd like to get varying opinions. I do realize that I might get hammered for this, but nonetheless...

On a rebound, player B1 has about a foot in-between the player he is responsible for, A1. B1 is between A1 and the basket as the ball comes to them. Its a little too high for B1's current position, headed over his head to A1 (who hasn't moved at all mind you). A1 goes straight up, and B1 jumps backwards and draws some contact with A1. B1 gets the rebound, and I tweet my whistle. Foul on B1.

HC for Team B is not happy, and proceeds to tell me "OK, your wrong on this one." (added just for emphasis).