BadNewsRef wroteIt wouldn't be a false double foul, because A1's actions would not be flagrant or intentional.
Plus, you can't penalize A1 for being pushed into B2 by B1.
A1 was fouled by B2 in the act of shooting...ball is live...
Presuming the lead calls a charging foul like it appears he does, you would then have a foul on A1 for charging and thus by rule a false double.
Now as a matter of practical application, I wouldn't imagine calling a foul on A1 for being pushed/bumped into a defender. That I agree.