Yes, because he behaved very strangly!Also he was very strong, pale, he had very weird eyes and he never appeared at folk when it was sunny!!!I think that these facts were enough to understand that he was a vampire!
I don't really know if I would say vampire. Okay, well, if he didn't say he was, but he did say that he HUNTED, then yeah. But it depends on what 你 mean 由 if the blurb never 说 that he was a vampire. It did give alot of hints though. But knowing me, I would probably be the stupid one and not get it because I haven't been into 吸血鬼 until now.