After some further research, it seems like it might actually be a digital painting, so it sort of is CG? I'm not very familiar with the terminology, http://www.vfxhq.com/1997/fifth.html has some details and mentions "digital matte paintings", but I'm not sure what's the difference between a digital matte and a typical CG background is. Maybe something to do with the rendering technology used, I dunno.
After some further research, it seems like it might actually be a digital painting, so it sort of is CG? I'm not very familiar with the terminology, http://www.vfxhq.com/1997/fifth.html has some details and mentions "digital matte paintings", but I'm not sure what's the difference between a digital matte and a typical CG background is. Maybe something to do with the rendering technology used, I dunno.