Next person who says "if it has two wings and 2 legs it can't be a dragon" gets tailslapped into a thin paste.
If you need an authority - here's a picture of Y Ddraig Aur, the gold dragon from Owain Glyndŵr's flag. If you can't trust an ancient Welshman to identify a dragon, then you can't trust anyone.
My actual feelings are that if someone stands up and says "I'm a dragon" I don't give a damn what they look like. A dragon isn't a species - it's an ideal of power, however that power manifests.