The transfusion theory is pretty unlikely. Floyd is right about that, though his reference to the delta ratio misses the point, since that is not well correlated with the actual amount of synthetic testosterone one takes.
The key number is the T/E ratio, and IIRC, Floyd’s was pretty high (10-20), which testosterone in a blood transfusion is very unlikely to account for. A typical transfusion would be about 5% of the blood volume, so that would imply that when he took the original testosterone, he had enough of it in his system to result in a T/E ratio of 200-400/1. I doubt very much that a rider mindful of being tested would take that much testosterone. If you look at the blood doping information that has come out, riders don’t take huge amounts of testosterone in that program. Moreover, Floyd’s quoted comments imply that he transfused several days or more before the positive test, which would imply an even higher initial level of testosterone.
This assumes he used whole blood. If he used isolated cells, there would be far less testosterone present, most of it being in the plasma. He might have injected the plasma, too—remember, that was the theory used to explain Contador’s positive—but again, the volume would be a fairly small fraction of the total blood volume.
I’ve never totally dismissed the possibility of a false positive, as some of his delta values were not as high as they should have been. OTOH, when USADA prepared for CAS, they obtained other samples from Floyd during that Tour, and some of the metabolites in those samples also had high T/E values. So the best explanation is that he was using T-patches regularly, and as 131313 says, he lied to avoid contradicting his earlier assertions. Best explanation, but still not one I’m 100% confident of.