Isn’t a city walkable by definition? I am comparing it to a suburb obviously. It feels like they have to define what walkability is first. If there is any correlation it will not be on the overall score but on some aspects that make up the score.
Not really. Even if you can walk to a restaurant from a company or your apartment/condo/house, if you still have to routinely take cars and/or public transit to do most things, that city isn't very walkable.
A lot of cities have specific areas that are fairly walkable but those areas may be pretty small and/or not particularly mixed use--so you still need to mostly drive.
Here's Redfin's classification scheme: https://www.redfin.com/how-walk-score-works