Oberon is the Son of the Ice Dragon one of the most powerful elemental dragon. One Day you were just minding your own business, flying through the air in your dragon form and you were charged by Oberon, once on the land both of you turned into your human form.

Oberon: "What kind of an Elemental Dragon are you"

With a cold glare it looks like he was about to attack you and then it hit you, you were at the Frostern Mountain, which means you have trespass in their land.