From the looks of it, what they're calculating is a net promoter score. The idea is that, in some context, what you actually want to know is whether your target audience would be willing to actually promote your business to their friends and family or not.

It's very common in retail and other competitive markets, because a customer that had an "okay" experience could still go to a competitor, so only customers who had a great experience (7+ out of ten) are actually loyal, returning clients.

Don't know if that's the best method to gather impressions on workplace environment though, I don't think many people would consider their workplace "amazing"