Yep.

Clan Pergamon had to move away from Arcane lands completely to recuperate from a rather disastrous choice of a living place, a mountain that was a hotspot for uncontrollable wild Arcane energies. Arcane born dragons weren't affected in any way as they were born to withstand that sort of thing, but anyone else who lived there long enough was going to either develop mutations or get sick and die.

Orestes himself as an Ice born was lucky in that he was young enough when he arrived to Arcane lands, but that the Mountain Keep wasn't his original "home" (as far as a street kid could have one.) That means he managed to develop some resistance to the natural Arcane energies during the years, so by the time he found himself at the Mountain Keep, the worst possible spot for non-Arcane dragons in the whole land, he was old enough to not be affected as badly as many others. So even though he lived there for decades, this small stub of a second tail is the only mutation he ever developed.

Also, he would not like you to see that tail, so I had to sacrifice myself to show it to you.