Quote Originally Posted by Kanti View Post
All the abilities in the dragoon storyline are thought up on the spot by the player. I am guessing they decided to dub it Blood of the Dragon because you get that ability after a certain part in the questline relating to said blood of dragons.

There's no explanation for why Paladin gets new abilities either. I'm not sure everything really needs lore justification.
In some cases we draw the knowledge from the Soul Crystal. As we get more intune with it and our discipline memories and knowledge surface from it. At least that seems to be what the it says when the skill is acquired.