The card's play instructions read: "Play just before you roll a Vailin Dragon's attack dice"
There is no constraint that you must be the attacker. Cards that actually do have such a constraint explicitly say so in their play instructions, so I'd say this is definitely referring to an attack roll.
So the question still lies: "When you're defending are your rolls considered Attack rolls?"
PLUS all things considered - if you look at the rules all dice are called ATTACK die.
I still don't think that answered the question, though.