My memory of the era is that no one would have thought they were actually 3d rendering in real time: that was Just Not Possible.

I'll point out that once they finally, FINALLY made a memory card for the Commodore 64, that plugged into the megabyte-per-second DMA port, there was a similar bouncing ball demo done for the C-64. Purely by loading whole frames into the memory card and blasting them onscreen as needed, like a page flip.