Im gonna go based on the content of their blood. So as the generation continues, a purebred's blood has not differentiated too much and contains 98-100% of a "pure" bloodline meaning no outsiders of where this purebred originated has mixed. A hybrid is where the original bloodline is mixed with many others, so while a purebred has 99% of the original bloodline and the hybrid has 50% and he other half belongs to an entirely different line.
I think it might be 2 but I could be mistaken sorry if I am
