No, it doesn't.
Literally nothing you've said suggests that Liam had any prior knowledge of vampires. He kills his family, yes, and his very, very Catholic father calls him a demon - not vampire, demon. It's the nature of the religion, especially the religion at that time. You see something that looks like Angelus, the first thing you're going to think is 'monster' or 'demon'. And saying that does not mean that you knew something like that existed before you were confronted with it.
In 'Spin the Bottle' he also accuses Lorne of being the devil. Does that mean he knows something about Lorne that we all missed? And he came to the conclusion that he must be a vampire only AFTER Gunn and Wesley explained that vampires are real. He made no such inference that he had any idea prior to those two spelling it out for them and only after Wesley mentioned the test that the Council puts them through.
Literally nothing you've said suggests that Liam had any prior knowledge of vampires. He kills his family, yes, and his very, very Catholic father calls him a demon - not vampire, demon. It's the nature of the religion, especially the religion at that time. You see something that looks like Angelus, the first thing you're going to think is 'monster' or 'demon'. And saying that does not mean that you knew something like that existed before you were confronted with it.
In 'Spin the Bottle' he also accuses Lorne of being the devil. Does that mean he knows something about Lorne that we all missed? And he came to the conclusion that he must be a vampire only AFTER Gunn and Wesley explained that vampires are real. He made no such inference that he had any idea prior to those two spelling it out for them and only after Wesley mentioned the test that the Council puts them through.