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...

Ai wouldnt bother doing that, but an editor who had limited footage would, and did. Look at the other segments, it’s all one shot that’s zoomed or played differently, to give the illusion of various shots to keep interest in the style of quick cut modern social media clips in vertical style. Watch for the red flag in other shots. It’s one lengthier clip we haven’t seen in entirety cut and zoomed and swept and reversed in differing ways.