All right, I think it's most plausible to assume DG was phrasing his statement somewhat carelessly, since he also said "there are things you can do only with blood" which would contradict his own statement of further down if taken literally.
As for what a "blood magic spell" is exactly, I've described the school of blood magic as a set of thematically connected spells that deal with mind control, demonology and manipulation of life essence. Those spells likely all involve blood in one way or the other, be it the Joining, creation of phylacteries, mind control or demon summoning. However, they may not need the blood to power them, but only as components. Which means they can theoretically be cast with normal mana, except that maybe the power requirements are so high that either lyrium or blood is needed to boost them. Specifically, this would apply to mind control and demon summoning, but not necessarily to creating phylacteries, demon containment like Malcolm Hawke did, or the Joining. Also, blood is a much more powerful boosting agent, and the amount of lyrium required may rarely be available to those who would use mind control or demon summoning anyway.