More comparisons. Original resolution of FFV was 240x224p. GBA version is 240x160p, meaning none of the image was lost horizontally, but vertically, the top/bottom 32 pixels were cropped. This isn't really a huge loss in practice though, and a worthy tradeoff for the much more detailed pixel art of that version. Pixel Remaster takes the 240x160p GBA assets, rescales them in some fashion, and makes new additions on the top and sides to expand it to a 16:9 aspect ratio. There are some new assets as well, like the background seen in this opening cutscene. As best I can tell, if compared to the original SNES resolution, it comes out to be something like 320x180p in practice. More of the SNES image is not retained, though, because they started with the GBA graphics, which were already cropped.
tl;dr the Pixel Remaster is like a revised GBA version graphically