Derek's reaction to her question is visceral. His expression scrunches with disgust and he shakes his head. "No," he spits out like it's a dirty word that tastes awful on his tongue. Drinking blood? That's disgusting and no, he isn't a vampire; the idea is so unsettling and repulsive to him that he can't help the grimace on his face.

After a moment, his expression softens into something more drawn again. "No. No drinking blood, I'm not a vampire."

Kate's last boyfriend had been a werewolf, Derek thinks, and she trapped his whole family in their home and set it on fire. Years later, she would regress his age so that he would trust her enough to let her into his family vault. In the in between times, she hunted him and even captured and tortured him once before Scott had found him.

Clearly, Buffy's confession that her last two boyfriends were vampires isn't comforting at all for Derek in his current position, vampire or not.