Having been on the "vivid imagery" spectrum I could easily superimpose images onto my vision. Now, after covid infection some years ago, I have aphantasia, so I can tell you it's a very real thing. A lot of the stuff mentioned in that guide is very true as well, I lost the "feeling" of my childhood memories for instance.

As I understand it, many (most?) people with phantasia can't really superimpose images onto their vision like this, but needs to close their eyes to imagine something, but I for sure could. I was fully aware not directly seeing it, the image is composed in the mind after all, but I guess a good analogy is you "playing music" onto music you're listening to. It's composed together in your mind, but you're fully aware only parts of it is coming through you ear.

Last, since you can imagine images in your minds eye like you describe, you clearly do not have aphantasia...