I can understand that, but the issue is a bit broader. The gas-liquid pumped around a freezer operates in a given range, and the lowest certified climate class starts at 10 deg but it can be 16 or 18deg.
Its very similar to the reason why a butane bottle just stops working at low tempertures while propane stays alive. It's the latent heat of vaporisaion needed to turn the liquid back into a gas that does the cooling. Thus lots of freezers working at 10deg will only achieve -16deg inside because it's outside its design parameters.
Maybe the Vestfrost does work at Zero despite its stated climate class. But having to heat a room to make a freezer work seems odd to me irrespective of warranty