Teaching the chef to make fried chicken isn't so much "repaying the favor[sic]" as sabotage.
Anyway, calling a dragon "Welsh" as a name is just messed up.  Funnily enough, said term originally just meant "Foreign", presumably since that was what the natives of Cymru were to a bunch of weird Danish invaders.  It was absolutely mutual, rest assured.   
Also he had better not start calling himself Pendragon.    That'd be like if I changed my surname to Miyamoto.   You just don't do that.  It ain't on.