I don't know if this is just me or I'm seeing things but when I turned on my G15T8 when I had it on for two hours (not being in there when it was on) and turned it off, I looked at it the second it turned off and the tube was glowing...Specifically where the arc traveled, I mean the afterglow did not fill the whole tube like it does with phosphor, it was a very definite afterglow

Anyone know how the UVC lamp has an afterglow?

Modern UVC lamps often have a very thin coating on the glass whose purpose is to prevent mercury being absorbed by the glass.  This helps slow the rate at which the glass turns grey over lifetime, and ensures maximum UV-C maintenance during life.  Depending on the exact coating that is being used by the manufacturer of your tube, it is possible that the coating has weak luminescent properties and might display an afterglow.