Corinnguard
Hero
Unless they were a polymorphed metallic dragon that was merely pretending to be the illiterate 25-year-old resident of a fictitious medieval village.Did you ask them, "Why would an illiterate 25-year-old resident of a fictitious Medieval village know the detailed biology and ethology of a rare monster that you, nor anyone you know, have never seen before?"


As for wanting to mix it up for the players, you can always use the dragons from a 5e-adjacent source or homebrew some dragons based off of an anime series like the Dragon's Blood Dota 2.
Eldwurms from Dragon's Blood Dota 2