No one said we were following the European interpretation of a dragon. And really it comes down to one’s artistic interpretation, the dragons in Skyrim are indeed dragons, but have the limbs of a wyvern, Their story and lore calls them dragons, so that is what they are.
If I want to write a story with an eight legged, four winged reptile and have that be a dragon for that story, then that is what it is. It is pointless to argue over one’s personal interpretation of mythological and fantasy creatures that are made up to begin with.
Different person, different opinions.
This is all from the mind of the viewer, and in the mind of most people, Wyvrens are a subspecies.
Also,
Many of these things are completely inapplicable to many stories.
Some stories may use this as a guide, but I have seen dragons with no wings, two legs, or eight legs and two wings, and even four wings and two legs, all classified as dragons.
In mythology and fantasy, rules go story to story, they never carry over entirely.