I dislike both Tesla and Musk but as an automotive company I'd wager they have good safety factors on at least most of their engineering, so for example in the name of keeping the battery from degrading too fast the tesla probably stops drawing power from the battery when the battery voltage drops to a certian number. The safety factor just means that the number it shuts off at is likely a good bit before the batrery would theoretically start to take damage.

I can't find any other reason they would intentionally keep range off the product, because its not like they selling a solution to it. So I assume they probably just lowered the voltage at which the Tesla stops drawing power because getting stuck in the hurricane was obviously more dangerous. I could be wrong though, this is just from my expirences with bateries in engineering applications.