It's entirely possible that the testosterone was real but not deliberate.
Tour riders get medication after every stage. IVs are common, and injections of vitamins and other things are common. As long as they aren't on the banned list, they're okay.
It's possible that somebody made a mistake in this regimen. Or there could be contamination in some sort of "natural" remedy - that has caught a number of athletes in the past.
The other alternative, of course, is that he *was* under regular injections, and either his natural level was a bit more elevated than normal, or he accidentally got multiple shots.
I would like to believe that Landis is innocent...