The textures were generated procedurally.  Unfortunately at 64x64, the resolution is low enough that the tiling becomes obvious across multiple adjacent textures (i.e. they don't look good).  Attached to this comment is a 64x64 version to demonstrate what I mean.

Manually slicing the 512x512 texture into an 8x8 set of textures is one possibility if you want to use the texture in an engine with 64x64 tiles.