Why does Andre, a vampire, laugh at Diana when she sees him outside of her apartment building?

At first Diana cannot believe she has seen an actual vampire outside her apartment building. When he reappears, she is prepared to fight him with the prescribed weapon, a cross. Andre merely laughs and grabs her wrist, explaining he has nothing to fear from the Son of God. It turns out that he is far from being a traditional vampire; he even apologizes for taking the blood he must drink to keep up his energies. As events go on, he becomes Diana's ally and lover.