I'm baffled that an author, who's entire fucking job is to visualize things in their mind's eye, both doesn't comprehend this and declares himself a 1 on this scale. Man writes fiction novels, how can he not at least consider himself a 2 or 3?
I'm a graphic designer with this issue. I'm highly creative but I never know what something I'm creating is going to look like until it is created. I bet you it's probably pretty similar with writing.
Because you can understand what's in a place and describe it without being able to see it. This isn't a skill you can develop, it's an innate feature of your mind whether you can actually see it like it's in front of you or not. I can visualize a complex scene in my mind, and not really write a great description, because those are entirely different things.