Major spoilers though, so tags to save you; you've been warned.
"Dovahkiin! No!!"
It certainly gives me the impression that he (who attacked Helgen) had no idea that you were Dragonborn until that point.
On an unrelated note he also at some point says during the battle itself "Thurri du hin sille ko Sovngarde!", but I can only speculate on what that might mean.
WOW
But I've not heard "No!!".

