It's possible, as the substance is used (illegally, IIRC) for that purpose, & the level of residues in the meat would probably be enough to account for Contador's test result.
Doesn't mean it's true, though.
To digress a little: the coverage of the Alain Baxter case included reports that the doctor who did his test had (Don Catlin, of the Olympic Analytical Laboratory at the University of California in Los Angeles) had delivered similar positive test results on many US athletes (including winners of rather a lot of Olympic medals) to the US Olympic Commission, which had decided that since the consumption was both accidental (according to the athletes) & probably insufficient to materially affect performance, no action should be taken against the athletes, and the results should be kept confidential. Hmm.
Athletics seems to have been dirty as hell, at least up to 2000.