Is there advantage in in-goal?

Five metres from the Pumas' line, the Blue Bulls tap a penalty, get the ball back and pass to the left where Dewald Potgieter knocks the ball forward and into the Pumas' in-goal where Elgar Watts of the Pumas swoops on the ball and moves to his left, presumably to kick clear.

The referee blows his whistle and orders a scrum for the knock-on.

There was a knock-on and the sanction for it is a scrum.

The Pumas then had to win the ball from the scrum and get it back to Watts for him to kick for touch.

This does not make sense. He already had the ball and probably had more room to kick for touch than he would have from a scrum.

Advantage in a situation like this certainly applies and it would have been wiser to wait to see what Watts did with the ball he had from the knock-on.