Given that one is a medication (antibiotic) and the other a water treatment, I can't really see how someone would come to that conclusion.
Copper, in proper concentration, has no effect on the fish, it's diluted into the water column to attack crypt in the free swimming stage of the Crypt lifecycle.
Antibiotics are completely different, in that they rid the fish of a bacterial infection. They can have an effect on the bio-filter, but metro. is tailored for anaerobic bacteria, that won't be present to any degree in a QT.