Your right, we are using data from geonames.org to build our Destinations DB and excludes islands and small towns. Also as to not require a lot of extra data for exact administrative boundaries for cities, etc PocketEarth is not always able to give the correct town name, sometimes picking a bigger city nearby. Using geonames data also has other downsides such as not correctly localizing place names to the user’s language.
We are working to replace our Destinations DB with information straight from OSM which will correct all of these issues!