Just a labeling issue. If you click on the 5k you get a detail popup on the right that says 5 miles, which is much more in line with several of the other times.

5 miles is not that uncommon a race distance in the US; 8k is very close, but you can still find both. (There are much fewer 3-mile or 6-mile races, those are mostly all 5ks and 10ks.) Though it's unclear if it was an organized race.

edit: it probably wasn't an organized race, there's a separate "races" tab.