It's entirely possible that the evil ex-watcher was full of it. Just because a character says something doesn't mean it's acurate--even if they're super-knowledgeable types.

I totally agree, but the plot is built on the idea that vampires really avoid Hanselstadt only because of the demon who feeds of regrets. As soon as Faith kills the monster, vampires, no longer restrained by his existence, attack the town, and Faith leads townsfolk into the fight.