"You met a what?" The Doctor reached out to try and take Amy's shoulders in his hands. If he managed to latch on, he'd hold her at arms' length and stare at her. "Fangs, blood drinking - was there an accent?" He might have been teasing her. Possibly. He might also have been genuinely surprised.
"Pond, that's brilliant. So, your vampire. Where did you meet him?" The Doctor did not ask if this vampire was of the people-eating variety. Amy had good instincts for people. She'd read him after only a very short time and she'd used what she'd seen to make the right decision when the Doctor was prepared to make the wrong one.
Amy Pond would not call a fellow a 'nice bloke' if she didn't believe it to be true.