Well, the chick grew up into a chicken, but you’re still not sure how the egg got into that cave...

Poupak was brought to the cave as an egg, stolen from a nearby farm, to feed the hatchlings.  But one of the little Mint dragons got confused and thought it was one of his.  He hid the egg away where the other dragons couldn't find it and kept it safe until it hatched, and grew up.  For some reason, since then, the adult dragons have decided to leave any chickens in the cave alone.  Poupak wanders around with the fierce creatures, eating scraps they leave behind, and sleeping with the hatchlings at night.