(the fairly realistic trees in that short are actually decals/impostors I think. still they look quite effective in context.)
The very first film-quality 3D graphics was all done on custom, one of a kind hardware. You can see pictures of some of it here:
Important to note, I think, is that those systems were not optimized around real-time display of models but pure rendering and high-resolution output ability. The scenes would have been developed using vector display terminals like tektronix 4014 or other similar things, almost entirely as wireframes.
Much early TV animation (for station IDs etc) was actually done on analog video synthesizers that had no 3D software, or really any software.
See pictures here
. They were often able to trick the eye and you may not have realized the difference. Analog animations were all done in real-time direct output to videotape, whereas the Triple-I/Omnibus productions were all scanned frame-by-frame directly to 35 or 70 mm film.