I am not sure what AR 60-8-22 says about the CAB. I believe that it says that the CMB is not to be awarded to officers above the rank of Colonel-and says the same about the CIB. There may not be any similar restriction on award of the CAB, but that is the only thing I can think of that might apply (other than the Kossacks being full of crap).
If that’s true he could have earned it a long time ago. Once you earn a medal it doesn’t go away. If your an enlisted type and earn a Good Conduct Ribbon and then become an officer you are still entitled to wear the Good Conduct Ribbon