Some are more used than others, and indeed, JPEG is an initialism. My point is the uppercase treatment doesn't depend on initialism, i.e. RAW doesn't have to stand for something to be capitalized because uppercasing file extensions is just a thing that happens.

The way I interpreted what they were saying is that they were focused more on the fact that for raw files, the extension is not ".raw", it's ".nef" (for Nikon for example) so that's why it's questionable to capitalize it.

“RAW file” makes sense when it’s an actual RAW file. However, raws come in a wide variety of other formats, too. DNG, NEF, X3F, RAF, just to name a few—all of these contain raw image data of some shape or form[0].

This project happens to be dealing not with RAW files, but with RAF files. (Even if it was indeed dealing with RAW files, there would still be a distinction between RAW as a file format and raw photos as a general concept, but we can safely sidestep that can of worms for now.)

[0] In fact, there isn’t even a precise definition or shared spec as to what constitutes a raw photo—it could be literally anything from debayered/denoised/prettified image to straight up sensor number dump in whatever way firmware feels like—which makes capitalising raw, as if it’s a specific thing, doubly silly when you’re not talking about a specific format.