I could always be wrong, but this sounds to me like a bureaucracy who - due to their own inertia and concerns that it may negatively impact next fiscal year's budget if it turns out that as many of the recipients as the lawmakers believe couldn't pass a whiz quiz - doesn't want to implement the drug screening at least as much as the recipients don't want their gub'mint goodies dependent upon passing a whiz quiz, and so they selected as many as they were reasonably sure could piss clean, seeded a few known positives, in order to make it look like the sampling might be truly "representative", and proceeded to do their best to structure the results so as to undermine the lawmaker's argument, so they'd shut up and leave them alone to their bureaucracies.