This is incorrect and outright wrong but he is on the right thinking track. Here’s why!
Salt, in itself, does nothing, I repeat, NOTHING to lower the temperature of any liquid, PERIOD.
What salt does allow is the ability to change the boiling or freezing point of water.
What this means, IF you can accomplish this, is the ability to get the cool can’s water below the freezing mark. This is a minor Benefit at best because the now colder than 32*F - 0*C water surrounds the fuel line for sure.
On the issue of how cold gasoline can be before it becomes frozen or even a slushy mix, I don’t know. Also, more food for thought, how dense can fuel get from chilling? A smart *** says, to the point where it starts to freeze, but is it any denser where a measurable gain is seen? AKA - Is it worth the effort?