I wouldn't call this a flaw, it happens to batteries when they are exposed to temperatures like this. The gauge for the battery is accurately trying to show you your usage in real-time.

I bet he probably could have gauged it by jumping in the car turning it on and then starting the heater as well. His mileage would have declined before he even started driving.

Think of it this way, batteries always improve in 2nd / 3rd gen devices (look at apple) and I am sure that is what Tesla will start to address.