Expanding out the stack here, Armvuan = Armbian + Devuan = ARM + Debian + Debian - systemd, so Armvuan = systemd-less Debian for ARM?
Not quite:
Armvuan = Armbian U Devuan = (Debian + ARM) U (Debian & ¬systemd) = Debian + ARM
Therefore: Armvuan == Armbian
If you look at the top of the file tree, Armbian is checked out as a submodule and forms the basis of the project. Also note that the commit history is short and makes no mention of Devuan: https://github.com/declassed-art/armvuan/commits/main