MC saw a dragon flying but had no idea it was Aileen/tower manager at the time since he hadn't interacted with her yet.
Much later after he saw the dragon flying, MC learned that Aileen had wings so he tried to guess Aileen's species....he guessed Aileen was a winged pig lol.
Aileen was upset at this and kind of stormed off.
TL;DR: as far as I can tell, this should be the first time MC learns she is a dragon