I have just watched the video clip of this incident, although it doesn’t show what the PK was given for.
The referee has his arm out for advantage Red; the mark of the PK was presumably the infield side of the ruck; red had won the ball and red #9 lifted the ball and moved to his left by 1 step. He then deliberately dropped/bounced the ball, so that the PK had to be given. The referee could not have played advantage!
Red #9 regathered the ball, started running towards the referee who was about 5m further infield from the ruck, and after 1 pace forward, red #9 dropped the ball onto his right foot. Because he was running, it looks as if the ball actually connects with his lower shin rather than his foot (although it isn’t clear), regathers and runs at a Blue defender who had not started to retreat and in fact moved forward in an attempt to stop red #9. Blue failed to prevent Red # 9 and he had a clear 10m run to the line, try given.
You could argue that Red should not have been allowed to take a quick since they had deliberately dropped the ball.
You can argue that the PK wasn’t taken at or behind the mark – but probably was taken with 1m/2m.
You can argue that the ball might not have been kicked - it was very close – but you cannot argue that the referee was in a very good position to see this and which is presumably why he allowed the try.