I am really not sure how we can even know if this condition really exists. I do paint from time to time and it often is humiliating how hard painting from memory actually is. If you painted a motive often enough, it is very easy, but I believe you access a different kind of memory than some composition of an imaginary scene. At some point you learn a technique how a shadow and shading of a certain surface looks and can add that to your memory or fantasy to generate a decent output. But if you just have an image in your head, it will be very difficult, even if you can "see" it very clearly.
Although I would recommend seeking a doctor if you can literally see things you summon up in your head, like I often read in articles.
Article is behind a paywall, so I just ranted against the headline instead.