It’s probably a mix. My freeway commute is fairly easy. Rush hour has gotten bad over the past ten years but I have flex time so I can stagger my hours so as to just miss rush hour both ways.
A fair amount of my Camry’s milage has also been 250-400 mile roundtrip mostly cruise-control freeway drives to the coast, where my children have been in college, or on vacations.
Cruise-control at freeway speeds does a lot to increase milage, especially if you stay below the speed where milage drops off sharply for a given vehicle (@ 73 mph for my Camry, but @ 67 mph for my Ford Freestyle).
I’ve been lucky that more than half my total Camry milage, perhaps as much as 2/3, has been on freeways with the cruise-control on. That has pushed my average mpg up close to the theoretical maximum.
That’s interesting you figured out where the most bang for the buck is on speed/mileage. As I said in a previous post the Civic will get 40 mpg when my wife is going along at 70, maybe 75, but it drops to 36-37 when I hover around 80. I have an Accord that was struggling to get 25 city but now it has limbered up and can get about 28. Highway mileage is similar to your Camry.