There is a defroster and it was working...you didn't see the tank-driver vision slit he was peeking through on final

If he had a TKS deicing system on the wings most likely he had a spray nozzle on the nose to shoot the fluid on the front window. I don't know if he elected not to use it for landing (because it restricts visibility...just like windshield wiper fluid on your car with no wipers!) and that's what built up since the last spray. It might have frozen over and all he had was his defroster up front powered by a small heater unit which burns a small amount of fuel to keep things toasty.
Either way...I wouldn't want to do that all winter long. I spent enough time being the guy on the tractor that I don't want to go up in that junk to take a box from A to B.