In November, when the NPC would run up to me and say this and ask for help, I was able to give them a Cure Disease potion to help them. That happened near Windhelm. Now, near Whiterun, it has happened 3 times but the only speech option is Sorry, I can't help you, even though I have Potion of Cure Disease to give them. It just makes me feel bad...hope the fix for this makes it into the next patch. Thanks!

Is the game not seeing that Cure Disease and Potion of Cure Disease (potion made by player) are the same thing? Is this the problem?

Yes, they will accept only the "store-bought" potions...

this is interesting considering out of near 300 hours.. I've never had anyone run up to me about being a vampire... actually i haven't really encountered all that many random interrupts. mostly just bad guys... Or good guys that want to sell me something, which i'll look... followed by trying to kill me but kill each other then go insane lol.... some screwed up npcs sometimes.