Remaster doesn’t change the original art or animation. Sometimes it is a rerender of original source files. Sometimes it is a treatment of the existing master files. It just adds fidelity to the picture and sometimes audio. Fixes things like low framerate, weird lighting effects, that kind of thing.
The intent is to make the distributed version more true to the real original. None of us got to see the original. The original is a bunch of data on various machines. What we saw was a low quality save file of the original, cut down and watered down to the specs of 4:3 CRT televisions and broadcast hardware of the time. That version develops artefacts not intended when distributed on modern media.
Now this probably isn’t using original source files but it is possible. Remaster as a term also is used when they take the final master copy and rerun it through more modern technologies to get a cleaner output which is what I expect happened here.
