If that's what they ruled that's one thing, but from what I see (below between about 3:17 & 3:20 shows the front on view pretty clearly I reckon) he doesn't pass it back, his left hand never leaves the ball. That doesn't make it a knock on, that makes it a bad pass.
There's nothing to say that a forward pass has to be to someone else, so that's still a forward pass in my opinion. It doesn't matter that it's accidental. I haven't seen an intentional forward pass called for a decade, so you'd have to then say that every forward pass that is called is accidental. I don't see it as being any different to when the marker reaches around and slaps the arm, not the ball, and the ball then dribbles forward from the dummy half.
The only thing I can think of is that the video ref can't rule on a forward pass. Since they can rule on that, then the only thing he could rule on was a knock on or an intentional lob over the defender, and I agree it wasn't either of those.