How do we know Dany isn't a warg too? Here is why I say she could be: Remember Robb's wolf bites off that guys fingers? Well it did that when it sensed the guy was getting upset. He didn't tell the wolf to attack, it just did. That's the same thing that happened when Bran was in his coma. And Robb intimidated Jaime with his direwolf without saying a word. Then you have Sansa's direwolf who somehow stayed when she told it too, even though I doubt she'd done much training. Look at the awkward way she was walking it, almost like she didn't really care. There seems to be a natural connection between the wolves and their owners. IF the Starks are all wargs (Jojen said it was in Bran's blood, which he happens to share with his siblings), that means that it's pretty typical of a warg to have a connection with their animal outside of direct control. Which is the same thing Dany has with her dragons. So maybe Dany is a warg too and the fact that the dragons are magical doesn't matter.
And I think he(she?) meant Bran is the strongest in terms of latent ability. Potential to be great.