Step back as a fixed phrase means "take a step back", but it can't be seen like this here.
Take a step back and translate it as: "leave temporarily" (not resign)
Step down and match: resign.
This sentence mainly uses two similar phrases, step down and step back, which have just the opposite meaning and create a sense of contrast.
The source of this sentence:/learningenglish/home/apple-Steve-jobs-takes-medical-leave-next-Google-chief-known-company-14761929.html.
Didn't the original text say: and Apple CEO Steve Jobs is on sick leave again?
It means that Jobs left his job temporarily due to illness.