It seems like the data isn't that accurate, if you look at Software Developers salaries on: https://swissdevjobs.ch/jobs/All/Zurich (and account for 25% taxes) you would end up with ~6800 USD.

And Software Developers in Zurich earn around the average salary: https://www.payscale.com/research/CH/Job=Software_Engineer/S...

They mention renting an apartment and then another chart is about:

"Based on cab rides, dinner/lunch for two at a pub or diner, soft drinks, two movie tickets and a couple of beers"

This seems a bit haphazard.