Couple of things......
Does the fresh water tank drain come off bottom or side of tank?
Off side...then some water may still be in tank. How much,,,depends on where on side of tank drain is installed.
Pump suction line may not go completely to bottom of tank leaving some water in tank. How much,,,,depends on length of pickup line
Water heater tank capacity is normally included in fresh water total.
All that being said.......even with a 10 gallon WH tank plus the 25 gallons you drained out of fresh water tank (total 35 gallons) you are still short 9 gallons
Contact MFG. (not dealer) and discuss your lack of fresh water capacity.
With your VIN they should be able to give you all specs. as built.