I just noticed the windows on my car are "nuclear blast proof" too. They survived every nuclear blast that happened since I got this car!
Doesn't really matter, it is just marketing. I guess somewhere through the design phase they did some calculations on how much force it can take and checked it against silly things for Musk to say.
The only point is that it's stronger than normal glass, which is backed up with the video comparing the two different types of glass in a more realistic scenario.
That seems like a meaningless claim without size and distance from the blast.