similar to IL2, format I'm bit familiar with -I guess global colormap defining types of overlaying textures (rock, snow, grass etc) transitioning one to other per that colormap (which of course could be grayscale) Also IIRC FarCry terrain editor used similar thing (did few maps for it back in the days) but of course used a lot of detail textures for close proximity to player, IIRC Chrome engine used similar way too (the first one at least) and some other titles. There are still tiling textures but not exactly the same these are now in example I don't think these would be rotating ones also transitions between types seem to be done in engine/map not on tile (good news!!!)
but that doesn't explain some sharp nice transitions between glacier ice and rock/volcanic rock ones visible in few areas on A-7 shot
edit: looking closely at new terrain shots -I have no idea in fact... looks like global hires texture