I've been back and forth over the video, and I cannot see any point where a black and a white player
"are on their feet, in physical contact, close around the ball on the ground".
The nearest I can get to it is this....
m
TP = Tackled player (his knee is grounded so the tackle has been made)
T = Tackler
TA = Tackle assist
AP1 is the first arriving player
The Black arriving player might be in physical contact with the tackler, but since the tackler is (by definition) not on his feet, he does not count for the purposes of forming a ruck.
A fraction of a second later...
...the Tackle Assist releases well before the Arriving Player can make contact with him. This was never anything other than a tackle. The conditions for a ruck were never met. Even so...
...the player who was eventually YC, treated it as a ruck and made every effort to get onside, stepping back to the goal line (further than he needed to go).
IMO, this was a completely incorrect call by the referee/AR. There was never any offside by White 11, who did everything correctly, within the Laws, and yet still got YC. Very hard done by.
Shoddy work by the officials concerned!