A demake would be a reimagining of a modern game into the style and aesthetics of the time. E.g. taking God of War and turning it into a 2D Shinobi-style platformer for Sega Genesis. Or turning Gran Turismo into a Mode7-style racer on SNES.
In this case, the creator wrote a custom 3D renderer and recreated the models/meshes to get as close of an approximation of the N64 experience onto the GBA.
I wouldn't call it a port necessarily ("recreation" seems more apt), but it's closer to that than a demake.
Interesting, I'm wondering if the GBA could handle a light version of a Minecraft style game, but the N64 looks like it could be great at it too. I need to get me a SummerCart64 one of these days and experiment with my old N64.
Related to this is the Atari Falcon port of Minecraft using a sparse voxel octree, might work for the GBA seeing as the Quake ports are similar performance-wise:
Affine texture mapping is kinda jarring to look at, especially in this GBA port since there is no fixup with huge ground polygons drifting around.
One of the listed features in the PS1 port in the OP article is tesselation to reduce the issues of the PS1 HW affine texture mapper, on the GBA you have some base cost of doing manual software texture mapping but also oppurtunities to do some minor perspective correction to lessen the worst effects (such as doing perspective correction during the clipping process).
Almost felt like the second video (despite being older) looked better in terms of texture jumping, looking closer now the wandering textures actually seems more to be more of an clipping issue than directly perspective correction related.
You’re misremembering. SM64 was fully textured, outside of specific models.
Also flat shading (vs. say gouraud shading) is isomorphic to the question of texture mapping, and concerns how lighting is calculated across the surface of the polygon. A polygon can be flat shaded and textured, flat shaded and untextured, smoothly shaded and textured, or smoothly shaded and untextured.