I didn't realize that Perl's package handling let's you "inherit" from a package that isn't actually a class.
There's no effective difference between a package and a class or a function and a method inside Perl 5. The internals don't care. If you treat something like a class name (by using it as an invocant), Perl 5 will use that package's namespace to find the destination method. Any reference blessed into a package will use that package's namespace to find its destination methods.
Those packages don't even have to exist for Perl 5 to attempt to dispatch to them as invocants, but you will get dispatch errors if they don't.