Yes, it does. Not linear larger files, but larger files at constant quality. His examples are conveniently chosen to sell his book. 20% bigger is 20% too much for a non essential asset.

Double image dimensions don't mean double file sizes, but they do mean larger file sizes.

If you've figured out how to display the same non-vector images at full quality at arbitrary file dimensions with the same filesize, then you're going to be very, very rich.