If I was coach A, I would have been upset that you didn't give a T to B1 for voluntarily leaving the court before the contact even occurred.
Seriously, if you are going to rule that B1 was not in legal guarding position because his foot was OOB, therefore putting him OOB, then it all depends on your definition of the "floor", since that is the word used in the legal guarding position rule - NF 4.23.1 - "Every player is entitled to a spot on the
floor... and also in the rule regarding player location - NF 4.35.2 - "When a player is touching ...out of bounds..., the player is located... out of bounds."
So I guess the question becomes, is a player who is OOB "on the floor" or not?