I have never, ever heard of case meaning mood before before and it doesn't really make sense. Nounal cases and verbal moods are two different things, hopefully that much is obvious.

I have, however, heard people corrected for mistaking case and mood - although one could be forgiven for making that mistake in Classic Arabic, where the two look exactly alike, inspite of their different purposes. (ًClassical Arabic, along with Modern Persian is my personal field of philological studies - the terminalogy used for both is the Latin one, though.)

Maybe it was a slip of the tongue on your professor's part?