Didnt see this yesterday. Have read all the various comments on here and made myself watch a replay just now.
My view as a showjumper is that it was what we would refer to as a "miss". We see this a lot in amateur showjumping – rider has horse on a very long one – horse thinks about popping in another stride, then in a split second realises there isn’t really room so snatches leading leg back and rather dives over fence. Usually accompanied by a sharp intake of breath, heart in the mouth moment for those watching. They get away with it SJ 99.9% of the time due to going so much slower and the fences at amateur level being very small, giving the horse a chance to "find another leg".
Difficult to tell from the replay, but it’s possible Darlan didn’t get a view of the hurdle soon enough, hence him changing his mind. I’m not an AP fan, however I wouldn’t blame him for this.