Documentation: What exactly is texture.channel for?

[Fennec]

This may be related to the material’s .lightMap and .aoMap properties.

.aoMap : Texture
The red channel of this texture is used as the ambient occlusion map. Default is null. The aoMap requires a second set of UVs.

How to use AOMap

If you check the code from that example, it’s modifying the model after loading it to add the second UV set: This is necessary for formats like OBJ where the file does not contain the AO map and it has to be added afterward.