I read that Russian Z didn't have any symbolism initially other than to make their armored vehicles easily distinguishable, especially from air. Could be that Rommel used same method to mark his tanks at some stage, in case they got caught in low visibility setting like a sand storm, and whichever Russian officer made a decision studied Rommels tactics and decided to use that. Or maybe specific units painted letters on their tanks to be easily distinguished and it's just a coincide that a Z one shoved up in the video, but I'm just guessing here.