The explanation is that that statement is incorrect.
The truth is the exact opposite: 1 gallon is comprised of 16 cups.
1 cup = 0.0625 gallons = 1/16 gallons
1 gallon = 16 cups 1 cup =0.23 gallon
no 1 gallon = 16 cups 1 cup = 0.06 Gallon
1 gallon = 16 cups 1 cup = 0.06 gallon
1 gallon = 16 cups 1 cup = 0.06 Gallon
1 gallon = 16 cups 1 cup = 0.06 gallon
1 gallon = 16 cups 1 cup = 0.06 gallon
1 US cup = 0.0625 US gallons 80 US cups = 5.0 US gallons
1 gallon = 16 cups 1 cup = 0.06 gallon
100 gallons 1 gallon = 16 cups 1 cup =0.23 gallon
1.6875 Gallons 1 gallon = 16 cups 1 cup = 0.06 gallon
10 gal 1 gallon = 16 cups 1 cup = 0.06 Gallon