I think all of us are "missing the boat" on this one! The antifreeze being used in almost every new marine application (and even some construction equipment) is using the new environmentally friendly Polypropylene Glycol (PG) antifreeze. Not the Ethylene Glycol (EG) antifreeze we are all accustomed to using. That being said, the antifreeze tester you might be using is not one for PG rather EG. The specific gravity between the two are different and would produce a false reading. So you might have the correct low temp reading. I really can't see Skiers Choice sending a boat out, especially to the Great White North with the improper concentration.
Celsius, what's that? Here in Southern Florida it doesn't get below 40'F; I can't even fathom -20'F.