Are High Priests really high?

[Peelee]

Didn't the Giant also say something about needing Skill Focus [Knowledge (Religion)] or something as well in order to have enough ranks to identify a vampire's dual-soul issue?

Not exactly.

The reasonings behind my stance:

Being a vampire is super-rare; being returned to life after being a vampire so you can share the logistics of how it worked from your point of view in such a way that it entered a general body of knowledge that people would have learned about in the course of their education is simply not something that has ever occurred.

My intended implication was that even among the clerics, this was not common knowledge