No, the cold spot is not the only wealthy census tract. There are many others. The reason the cold spot stands out is that there is a good probability that it is cold because of some process there, not random chance.

The other areas don't appear as significant cold spots because the dispersion (not concentration) of homicides there is random. Or, looking at it a different way, the variance in homicide rates in those wealthy areas that are not cold spots is not explained by wealth.

Also, the cold spot in question is low in population, with only a few families living there. Those families have at least one child each, bringing down the median age. The tract is also made up of a major park, so it is not too populated.

This is what I mean by needing to know the place more than just the numbers.