Watch people draw, and you'll realize that can't be true, or at least is a very incomplete description of what's going on.
People have processes they go through to eventually get to something reasonably correct. Systems for drawing people, perspective rules, etc. These get extremely elaborate. They shouldn't need any of it if they could fully visualize the scene. They'd just need to copy that image to paper.
You'll hear people say things like "trust the process". They are struggling with what they're drawing looking wrong to them, until they're fairly far along and the shapes are fairly complete. Even when they're doing things correctly, their brain isn't recognizing it.
> They are struggling with what they're drawing looking wrong to them, until they're fairly far along and the shapes are fairly complete.
In general I agree, but I have a counter example. I have a friend that has always been very good at drawing, and when he draws, it's immediately obvious that he has a very precise idea of what is going to happen. People often gather around him because it is entertaining to look at the drawing and suddenly understand what it represents. It's a similar experience to uncovering a photo frame covered with dust.
I assume that this ability is not uncommon among professional drawers.