Expansions used to come in disk form, you know. They're not exclusively downloadable. And mods aren't always expansions. Each word contributes something different, even if they have quite a bit of overlap and are often considered synonymous these days.
The thing that gets me is calling it DLC-sized. So... small? Large? Is it horse armor sized or Shadow of the Erdtree sized DLC? DLC is not a unit of measurement.