I think the ref was asking whether the winger caught the pass cleanly, given that it was close to the ground when he caught it; thus asking the vr to see if the ball had been knocked forward by the catcher, not if it had been passed forward by the passer.

How come a forward pass is not off side - surely the reciepient is front of the last person to touch the ball?

Depending on how far the ball travels it is perfectly possible to be behind the person passing and to catch the ball in front of the point of release.
This general topic has been done to death. Once again I refer everyone to the RFU video explaining how a ball can go backwards from the hand and still go forward relative to the ground. One further development to the topic is that with a Hawkeye like system it should be possible to factor in the speed of forward motion by the player to calculate if the forward movement of the ball was in line with a ball that had gone backwards from the hand. Then I thought for God's sake just get a grip.

They would only be offside if they were in from when the ball was passed. Similar to a kick, if you chip over the top and a chasing player gathers they are in front of the last person to touch the ball.

A knock on is forward in relation to the pitch.
A forward pass is in relation to the player.
Camera angles can't pick up on forward passes very well, but can on knock ons.

Saying that, I still think video ref should be able to judge forward passes. They have plenty of angles to judge from.

For me that first try was a clear knock forward. There was no 'pass' as he was just batting the ball, and IMO it clearly went forwards as the on field ref thought. Wouldn't have changed the result but a bad early call nonetheless.