Maybe those files have been compressed using Cromfs: Compressed ROM filesystem for Linux (user-space)
. At least, that's what the file command says:
$ file root.fs.v5
root.fs.v5: Linux Compressed ROM File System data, little endian size 76468224 version #2 sorted_dirs CRC 0x9c06a023, edition 0, 30018 blocks, 459 files
I'm trying to install cromfs and see if it works...