He was reported by TSA because of the way he was acting. So this case didn't have anything to do with random tests nor an observation by company.
Here's the part that has me scratching my head: After the FO was handcuffed on the apron
in full view of the passengers, the flight was cancelled due to a "problem with the co-pilot chair".
Source. I wonder what problem that might have been? Either the "problem with the chair" was the simple fact that it was now unoccupied, or possibly the chair was... soiled.