The way they calculate these is a bit odd. The last time I looked at the list, there was a neighborhood in Jacksonville, FL listed, so I looked at it.
It wasn’t an entire zip code, just a section of the city that had a distinct geography. Further, it was mainly an abandoned commercial area in the middle of a rough part of the city. The only residents (<800) were in a single apartment complex at the corner, which was functionally part of a different neighborhood.
In short, a lot of drug deals were being made and going bad (and bodies dumped), but likely no more than in the surrounding areas, but the low number of residents made it jump way up by crimes per 1000.
The way they calculate is a bit odd
From what you describe, it is. A meaninful list would look for clusters of various crimes, and list the most saturated clusters as the most dangerous areas, whatever the population, zip code, or within one locality. Whatever the population is in those areas saturated with crime is doesn't really impact their danger. The population does not affect your safefy individually when you're in that area.