Likely reversed because whoever edited these clips together wanted the camera to be moving consistently forward. If they didn’t reverse the middle clip it would give the impression that the camera was moving forward, then backward, then forward again. Editor probably figured most viewers would likely focus their attention on the waving flag and not notice the backwards walking. I didn’t notice until I saw your comment and rewatched the clip!

Edit: but then there’s a backwards camera move at the end, so now I’m questioning my own theory…