If your build process always produces the exact same binaries, and you always use the exact same environment to run these, then yes, that's reproducible. It's not equivalent though, in that you can easily have a system that always exhibits the same behaviour (what NixOS does) but does not use bit-by-bit equal binaries. For example, some symbols in some library's .so file might be in a different order, or some padding bits that are never read might be zero or random depending on your compiler's choice.