Another theory might be that he did indeed take it, told Gus the truth but Gus is leaning on the false positive stats (however low the % is) and any other anomalies that can and do happen. Play the "I'm standing myself down for the good of the team" card, as opposed to being stood down by the...
If that's the case then they'll probably change it again.
And yes it's exciting to finally talk about finals again. Just gotta get through this week first...