Hard to tell, honestly. I see 3 possible points of contact on the play: 1st is the right hand trying to push perk out of bounds; this happens throughout the play. On the one hand, it may be made worse by Perk falling backwards himself; on the other, he clearly extends his arm all the way. 2nd is Gasol swiping Perks' wrist as Perk is passing the ball. 3rd is that same hand on the follow through gets an extra push in at Perk's face.
So honestly, I'm not surprised it wasn't a flagrant, but on the other hand, it was not a basketball play, especially when you combine the straight-arm push out of bounds with the right hand with the extra left-hand swipe at Perk's face, which to me was clearly antagonistic. Considering that Perk's incidental elbow stood as a technical and Pierce's extracurricular shove on Redick was upgraded to a flagrant 1, and that that is exactly the type of extraneous foul that can lead to ugly retaliation, I wouldn't be surprised to see it raised to a flagrant 1.