Earlier in this very same chapter, Harry tells Quirrell that he can’t imagine Quirrell hurting someone unless he means to. (This was in context of their discussion of the Gryffindor who cast a dark curse without knowing what it did.)
So we can assume that either Quirrell isn’t as precise as Harry thinks and accidentally hurt Harry, or that he’s exactly as precise as Harry thinks and took the blood on purpose.
Earlier in this very same chapter, Harry tells Quirrell that he can’t imagine Quirrell hurting someone unless he means to. (This was in context of their discussion of the Gryffindor who cast a dark curse without knowing what it did.)
So we can assume that either Quirrell isn’t as precise as Harry thinks and accidentally hurt Harry, or that he’s exactly as precise as Harry thinks and took the blood on purpose.