The new Vampire feeding animations and the addition of Crossbows suggest that we will be hunting Vampires however I must admit I am not quite sure what to make of the Snow Elf entries.
My guess would be that the Dawnguard are a faction of Vampire Hunters that the player will be able to join when the DLC is released and the DLC will focus on hunting vampires, suggesting anything beyond that would require a stretch of the imagination.
Personally I am hoping for something akin to the old gothic horror dracula stories with an isolated village tormented by the minions of darkness and the player being tasked with finding the secret behind the Snow Prince's curse.
A friend of mine told me this morning that the NBA halftime show had a trailer for Dawnguard and blackops 2. I'll go google it. I'm posting on my phone so I haven't had a good chance to do so.
I would say that there is a good chance that your friend is a liar.