Very few E-4s retire from their respective services, as the rules usually call for one being an E-6 to retire. There are limited exceptions to that, but I doubt that this is one of those.
Seems weird that it could be considered a retirement. There would be lots of retired workers by that definition. I always understood military retirement to be something greater than two enlistments. Not sure why but that always stuck with me. I think it was the idea was anything over two enlistments was a career and under was simply ‘two enlistments.”
Not to in any way minimize two enlistments.