memes

"Dragons are reptiles" Ehhhhh... I mean the first ever creatures to be referred to as "drakon" are just big snakes, so yes, but every others ? They're chimeras with reptiles and non-reptile elements, so I don't think they can be properly classified. The Drac from occitan folklore is for example almost always depicted with mammal-like ears. Even the Welsh Ddraig has ears, you ca see it on their flag: I think this remained common until recently, when people started taking Darwin's orginin of species into account and make dragons that might nicely fit into a classification of species. Bat wings an horns are also traits borrowed to mammals. Not strictly "mammalian traits" because we can find examples of reptiles that have had similar features, but clearly these medieval people didn't think "It's a mix between a dimorphodon and a carnotaurus !".

This chimera aspect is even more important and Chinese dragons which are described with nine ressemblances:

as to the nine resemblances, they are the following: his antlers resemble those of a stag, his head that of a camel, his eyes those of a demon, his neck that of a snake, his belly that of a clam (shen, 蜃), his scales those of a carp, his claws those of an eagle, his soles those of a tiger, his ears those of a cow. Upon his head, he has a thing like a broad eminence (a big lump), called [chimu] (尺木). If a dragon has no [chimu], he cannot ascend to the sky.

~quote attributed to Wang Fu, via Wikipedia.

Of these nine animals, only the snake is commonly understood as a reptile. Cladistically speaking, the eagle is also one, but that's still only two out of nine. And four mammals (assuming the demon isn't one... I'll take it it's also non-classifiable).

So, dragons aren't strictly speaking reptiles, and giving them mammalian traits is acceptable and trivial.