Compositing means you can excuse an extra dozen megabytes per megapixel of window size. The window in the article is less than a megapixel. That factors in the relevant part of screen resolution too. High resolution assets should scale alongside window size too, adding a fraction of the above dozen megabytes.

And I'm saying 98SE already had image-heavy design sensibilities all over.

You don't have to highly hand optimize to run a weather UI in a lean way.