I noticed they included most all the tiny regional airports in Iceland, but left out ones like Kulusuk in Greenland, which receives international air traffic.
Receiving international traffic is actually not a good measure of an airport's significance. Grand View International (WN23), for example, receives international traffic (from Canada), but has only a single 1700-foot grass runway. (It's also private.)
LHPR does a lot of business for Audi, 33 000 passengers a year between the Hungarian factory and the Ingolstadt parent plant in Germany and also some cargo as well. There are charters as well. So it receives international air traffic, alright but there are no scheduled flights simply because the area airports have no capacity problems. With three capitals -- Vienna, Budapest and Bratislava -- all within an hours drive in an imaginary scenario where those would be congested it would be booming but this is not London.
That is weird indeed. Especially since there are regular scheduled flights from the Reykjavík airport[1] to Kulusuk. Reykjavík airport is included, along with most airports that have scheduled flights from there (like Ísafjörður and Egilsstaðir) but not Kulusuk.
[1]: not to be confused with the larger Keflavík international airport that handles almost all international flights to Iceland
