He was doing 3d tile mapping but a major component for him is to have each vertice of a portion of the mesh conceptually equivillent to a tile. Have a separate uv data set so that each tile may have interchangeable textures or texture coordinates. Yet the whole thing maps to a contiguous mesh and is built as one.
E,g, if you have a mesh with 6 vertices were vertices 0 to 3 make up quad 1 and vertices 2 to 5 make up quad2 then the shared uv coordinates at vertices 2 and 3 wont allow you to use two separate tiles in that mesh. This can be done with multi texturing and more data per vertice but then that starts to represent a whole unacceptably whole lot of data for all adjoining sides and possibly even more if the mesh is not comprised of grids.
So he was attempting to separate the quads and align them so that the edges of a quad 1 which is then made up off vertices 0 to 3 touch the ends of another quad made up of vertices 4 to 7 so each has its own separate uv components.
This would all be trivial if it were possible to attach uv coordinates to index data instead of the vertice data itself but as far as i know that’s not possible.
The point of this would then be to make a 3 dimensional tilemap / heightmap / model just like any 2d map were you could place tiles at a location with arbitrary textures coordinates or even different textures as well however the entire thing would be in 3d model form. Though the edges getting artifacts can be difficult to deal with when having the vertices not truly shared.
I had been meaning to write a version of that mesh class that will do that for tilemapping but i just never had the time or need as of yet.
I linked to it as he might alter it to do what he wants with a bit of effort.