The CZAR is a skorpion receiver that uses an AR FCG. Naturally that means the bottom looks AR-ish. There are two versions; v2 is basically v1 but with a pic rail in the back instead of the original buffer tube holder.
The czar is probably an evolution of FMDA's earlier skorpion frame found here: https://github.com/maduce/fosscad-repo/tree/master/Pistols/Skorpion_vz61_Lower_Receiver-FreeMenDontAsk. There was also an earlier version of the czar named the skar I think that seems to have disappeard from the internet.
https://ctrlpew.com/the-czar-3d-printable-vz61-receiver/
https://ctrlpew.com/file-drop-czar-v2/