He's referring to the sequence starting at 4:15. Compare the close up real time shot that starts the later sequence to the slow motion at 2:52. The feather and ball leave the frame almost simultaneously in the earlier one but with ~25% of the feather still in frame in the latter.
After looking at it I agree with zwp, the editor really did make quite a mistake when assembling the last sequence.
[Edit: Screen grab of both http://imgur.com/EAKB5FK and I agree with the over all editing comment below. The slow motion shot as the first shot of falling in the vacuum was the thing that really stood out and I thought was bad on the first play through.]
Oh, I see what you mean now. Yes, definitely editing mistake :-). Apart from that, editing was bad altogether. There should have been many shots with the real-time fall. In fact, the first shot of the drop should have been in real-time.
After looking at it I agree with zwp, the editor really did make quite a mistake when assembling the last sequence.
[Edit: Screen grab of both http://imgur.com/EAKB5FK and I agree with the over all editing comment below. The slow motion shot as the first shot of falling in the vacuum was the thing that really stood out and I thought was bad on the first play through.]