Hello! thanks so much.
First of all, the game uses a combination of custom (self-made) 3D assets and pre-made low poly assets. The stylized look does not come from the models or textures themselves, which are just plain albedo textures with no normal maps, height maps, cavity maps, etc. That look is 90% obtained from shader magic and post-processing. So the pipeline is very simple: model with few polygons, plain flat color (zero shading) albedo texture, and let the shaders and post-processing do the magic.