It's especially hard to express "happiness" across languages. It's a word that is hard to define and generally has no perfect synonyms between languages. It ranges broadly from "present feeling of contentment" to "ultimate feeling of fulfillment in life," and it seems like the survey is aiming for the latter aspect. Therefore the ladder analogy is a decent way to communicate that.

This isn’t gauging happiness but rather if your country is fulfilling your aspirations. I bet someone that works in a role he didn’t really want still might be very happy on a day to day basis but he never had the chance to become the doctor or botanist he always wanted to be.