Way Better MPG Than Expected.

I have a 2017 Turbo’ed 6-speed. I drive about 5-6 times a week, 4 days to work, which is an 8-mile drive one way. 1-2 times for errands, usually 5-10 but up to 15-mile trips. I can get almost 420 miles on a full tank. And usually average 35-40 mpg. The best I've ever gotten was 48.8 mpg. (Grandma Driving) This was initially shocking to me because I drive fast, don’t use eco mode, and when I bought the car, the mpg was quoted at 25/31. I was also told the auto version of my car was better, getting 27/33. Now I’m just trying to figure out why I’m getting better gas mileage than quoted and even better than my automatic counterpart.