Being "Overemployed" by holding two or more jobs at once, (which is not what that word means, at all) is not unethical. Many of the "tips and tricks" posted there are unethical. That's what the author said.
>2.08. Accept no outside work detrimental to the work they perform for their primary employer.
After 40 hours, your Quality tanks. Period.
It is absolutely unethical.