The low tile count simply comes from applying the dual grid approach popularized (if not invented) by Oskar Stålberg to a specific 2d perspective where tiles can be generated through rotations and/or flips.
Oskar does both rotations and flips to his 3D tiles, albeit only in 2 dimensions. He uses basically the same set of 5 tile shapes for any tiles that don't need to take into account verticality (i.e. look at the beach tiles in Bad North)
Oskar does both rotations and flips to his 3D tiles, albeit only in 2 dimensions. He uses basically the same set of 5 tile shapes for any tiles that don't need to take into account verticality (i.e. look at the beach tiles in Bad North)