I found that one as well before my reply that the quoted weight was correct. My error was assuming the density is 1.0. That works fine when measuring in grams vs cubic centimeters. I was surprised to hear that 8 lbs of water isn’t volumetrically a gallon.
I remember from chemistry class that it is 1.0g/mL and for some reason I thought it was 8.1 lbs. per gallon but I was wrong too until I double checked what that guy said. So now I know that it is about 8.33. Live and learn!