Zproject is not a build system. It's more like package.json esque thing for C. We used it on a past and it was capable to generate auto tools (or c make) build recipes, Debian or rpm packaging, ffi bindings and more.
But you're right it got almost zero traction outside of zeromq.
I'll point out that the article was written "2430 days ago" and uses a CMakeLists.txt example that looks like it.
The article then goes on to announce Yet Another Build System that doesn't seem to have gotten any traction.