From 38mpg to 45mpg on 07 hatchback by hypermiling and detailing exterior

[tmontague]

Iirc a few years ago there was a test done and it was found that a clean car will achieve better mpg. Lots of surface area paired with a smooth surface can do a lot. I don't think it alone is the reason for the op's very high increase in mileage but it has been shown to help and there is a definite plausible mechanism of action