Was it forward? Was it a knock-on?

The Blue Bulls attack and decide to go wide. Scrumhalf Ruan Snyman passes to flyhalf Jacques-Louis Potgieter who sends a long pass to Stefan Watermeyer. Stephan Dippenaar cuts in towards Watermeyer who tries to give him a short pass. The ball strikes Dippenaar's right hand and comes back to Watermeyer who runs round Dippenaar to score.

The angles are not easy and that interplay between Watermeyer and Dippenaar happens in the twinkling of an eye.

Was the little pass from Watermeyer to Dippenaar forward?

Hard to tell.

When the ball struck Dippenaar's hand did it go forward?

Probably not.

If it had gone forward off Dippenaar's hand it would have been a knock-on even though Watermeyer caught it before it touched the ground.

Law 12 DEFINITION
A knock-on occurs when a player loses possession of the ball and it goes forward, or when a player hits the ball forward with the hand or arm, or when the ball hits the hand or arm and goes forward, and the ball touches the ground or another player before the original player can catch it.
‘Forward’ means towards the opposing team’s dead ball line.

It may have looked wrong but in all probability was not wrong and the referee - bless him - did not guess.