OpenHouse explained really well! Also to add on:
The white patch is very bright, and draws your eyes to it instead of the subject of the photo (the explorers), which is a lot more in shadow. Even if I'm looking at the explorers, my eyes move toward the white patch anyway. If you kind of blur your eyes while looking at it, you can definitely see what catches your eye the most, and that's probably what people find distracting.
On a separate note, I really like the vibe from the photo! It brings to mind memories of exploring all day with people and deciding to watch the sunset together