It was pseudo-3D, I remember reading an article about how they made the sprites, but can't find that... wikipedia has

Donkey Kong Country was one of the first games for a mainstream home video game console to use pre-rendered 3D graphics

and they used SGI workstations to create the models and animations before compressing/converting them to 2D sprites

Rare invested their NES profit in Silicon Graphics, Inc. (SGI) Challenge workstations with Alias rendering software to render 3D models. It was a significant risk, as each workstation cost £80,000.

(sharing bc I thought that's a crazy amount of money for 1992)

IMO, that's all a part of the Rare+Nintendo hype at the time. Killer Instinct was in the same campaign for these pre-rendered 3D graphics as the wave of the future. Don't forget, they had to go toe-to-toe with Sony's Playstationat that time, so bringing anything that looked like real 3D on a SNES was kind of a big deal.

In that era you had CRTs or Rear Projection TVs.

Rear Projection was bigger (55" 4:3) but often times was susceptible to burn-in and had a worse quality picture compared to a CRT

Before LCDs it was plasma which until the the late 2000s had more technical advantages over LCD Refresh rate, contrast. LCDs couldn't really match them until the 2010s (I never had a plasma display though so I don't fully understand plasma)

DLP was a thing and could get up to and over 80" while maintaining quality but DLP could not be wall mounted as they were quite big like rear projection screens