Why do they make you think Robert Carradine is the Vampire?

[Handofdoom71]

In the movie Mom's Got a Date With a Vampire close to the beginning, they try to make you think Robert Carradine is the Vampire, making obvious hints to it. Then they bring in Charles S. and pass him off as a random guy named Demitri. Then they make it turn out that Demitri is the Vampire, who we thought turned out to be Wolfsbane. We are under the impression that Robert Carradine is Wolfsbane, AKA the Vampire, but it turns out that Demitri was the Vampire. But, past the point where we are introduced to Demitri, we are still under the thought that Carradine was INDEED the Vampire. Why did they do that?

[Disney Duster]

I don't remember how the movie went, I only watched it once or twice, but do you know filmakers often try to make the audience think one thing so they can surprise them with something different? And scary films often rely on mystery, not knowing about the scary being, and scary surprises.