This is prior to any contact. O'Mahony is being hoisted up and backwards, the ball is ending up behind him and even without contact from Folau it's going to be difficult for Stander to bring him to ground safely.
A couple of frames later and Folau's left arm has made contact under the left armpit of O'Mahony as he competes for the ball. At this stage though O'Mahony's position in the air is entirely due to Stander and the fact that the position he has jumped from was in front of the ball and he has to go over backwards to be in a position to catch it.
Folau is about to be the one that wins the contest by slapping the ball back towards the Wallabies side.
Folau's right hand never grabs or pulls at O'Mahony. Without the reverse angle it is impossible to tell how much force his left arm has put on O'Mahony.
Here, Stander is still propelling O'Mahony up and backwards and has no control over him.
Folau's left arm has made contact and even slight contact in an uncontrolled single man lift is going to be enough force to make things dangerous.
We need that reverse angle to see whether Folau has grabbed or how much contact has been made. I agree that he is in trouble but I think a major part of the problem here is that I think there is nothing more than incidental contact between two players competing for the ball in the air but the problem is that they are both travelling in the same direction whereas the forces tend to get balanced out when they are both heading towards the ball.
Clearly Folau was in a realistic position to contest because he is the one that slapped the ball back. This type of lift where the player is uncontrolled and going backwards means that even the slightest incidental contact will create a dangerous situation.