S2E1 and the evidence for code detection

I was just rewatching S2E1 and realized that the fact that Mark W was caught with Mark S's note is at least very strong evidence that the code detectors are real, right? I mean, yes it's theoretically possible that Mark W found the note on his own and reported it, but that seems very unlikely. The note was dropped minutes before Mark W had to leave and the way they all reacted the next day seemed very clear that he was caught with it.