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.