Makes no sense, the wording suggests it can use Homebrew's backend, not that it's a complete alternative to Homebrew. Nobody is confused about that.
I mean, I'm confused about it. The nanobrew homepage says this:
> nanobrew
> The fastest macOS package manager. Written in Zig.
> 3.5ms warm install time
> 7,000x faster than Homebrew · faster than echo
It presents itself as an alternative to Homebrew.
The recipes for building and installing homebrew packages are written in Ruby
You cannot really be compatible with this unless you run the Ruby as the install scripts could do whatever arbitrary computations
In reality most recipes contain a simple declarative config but nothing stops you from doing Ruby in there.
Hence to achieve total compatibility one would need to run Ruby