There's something comforting about having Willow around, something that's absent in others from home who tend to regard him with suspicion and unease. Drusilla doesn't count, for that confidence she has in him was instilled in her by he, himself, for twisted purposes he didn't like to think about. Willow seems to have a unique spot in Angel's small circle of lasting connections in being the only person from Sunnydale who has that kind of faith in him and trusts him. He values that beyond words' ability to express.

"Thank you. I appreciate that." He hesitates, then asks, "...what kind of blood is it?"

Human, he can do. Human he's done more often than he's detailed to those around him, and not just counting the time River was in his body and went on a human blood drinking binge fest that left him feeling anxious and wound up with energy that had no release for a good month after his body was returned to him. When he got hurt badly, it was human he drank. Animal blood didn't quite do it when it came to helping him heal in the ways he ought to, both with precision and time.

If the blood they'd been supplied with was human, he wanted to be prepared to deal with the judging sort of backlash that would come with it, for it seemed like anything remotely associated with his soulless side turned him into some ticking time bomb in the eyes of others whenever he came in contact with it.