Dead ball contact

First half, I am Trail opposite. 5 seconds left in the first half. Black takes the sideline inbound pass and drives up the court. B1 beats his primary defender, A1. A1 runs to catch up, and tries to swat the ball away from B1. A1 fouls B1 on the arm, who loses the ball. Clock stops at .9 seconds. After my whistle A1 keeps running past B1 and runs into B2 who is at the 3 point line. I cannot see B2 because I am being screened by B1. There is contact between A1 and B2 and A1 ends up on the floor. I hold my original foul call and look to my partners to see if they saw what led to the contact between A1 and B2. We don't gather, and after a few seconds I simply take the 1st foul to the table. At halftime I asked my partners and neither of them saw whether B2 set a legal screen that A1 ran into, or if B2 gave A1 a forearm (which is what A1 was claiming). Neither coach gave me any problems when I reported the foul, and we administered the bonus with B1 shooting.

Absent knowledge of how the dead-ball contact between A1 and B2 occurred, was I right to not call a technical? I felt that B1 was a secondary screener -- would this dead ball contact be Lead's call?