I suppose you could argue that, but it is not a package manager in the traditional sense.
My main point here is that once you build the system, there is no longer any notion of "package", just files that make up your root filesystem. There is no package database tracking which files came from which packages. Instead, if you want to add/remove/update a package, you rebuild the system with a different specification, and then sync the resulting tree it to /.
> Instead, you configure a set of specifications of what files from which packages to include on your system
Isn't that a just a declarative package manager?