
No other defender is in any kind of position to have been able to knock the ball out of his possession. As you can clearly see, the tackler is well underneath the ball-carrier, so it's rather evident that he couldn't do it. I'm sorry, but this thing is not anywhere remotely close to being a fumble! I still say IFP! 
Fumbles (loss of possession) can occur by other means than the ball being knock out by an opponent - for example, unsuccessful attempt to transfer the ball to another position.
As noted earlier in this thread, no question the loose ball goes forward. The issue is whether the ball carrier
threw it. If he did, it's a foul. Just as with any foul, the calling official must see the foul occur before flagging it. "Seeing" this particular foul means actually observing B45 throw the ball. Do we unequivocally see him propel the ball from the palm on his hand/s? Even in slo-mo, I don't believe this video shows that.