Very well the perp was barricaded behind the counter and the FB’s were thrown behind that counter.
Guess we don’t know without knowing what exactly is on the other side of that door. Is it directly into the shop, or some kind of common access service area?
Picture this: Assault team goes thru the door and advances into the building only to be shot in the back by bad guy concealed against the the wall they just passed. The initial team knows the flash bangs come right behind them to dis-orient anyone the may have passed. It’s possible that this is the swat teams strategy.