I would have to relook at the video, but I believe the person on the sidewalk was within his possible line of play. That course gets a lot of activity as the city won't let them close it down for the tournaments. The sidewalks are really close to the line of play for many holes. While they are pros, they still do have grip lock/shank issues or even plan on throwing over the OB sidewalks. So, that could have been why he waited. It is normal to wait for people using the sidewalks to ensure there's no way to hit them. It's happened a few times and unfortunately many users of the park are wearing headphones/earbuds and can't hear a player yell fore. And many of them don't even know what that means. I've seen people get hit and I've heard tales of it. One year, the city made Spinners close down one of the holes prior to the Memorial because someone practicing the hole hit a walker and the walker ended up getting stitches and filing a complaint (maybe a lawsuit) with the city.
Anyways, the field of play can sometimes be outside your intended line.