The wording is likely the source of the confusion. The section says “4:3 and similar frames,” not that every image on the page is strictly 4:3.

From the examples described, several images are actually showing 3:2 or 2:3 compositions for comparison, alongside discussion of lower aspect ratios such as 4:3 or 5:4. In other words, the page appears to be illustrating the idea of squarer versus more rectangular frames, not presenting only 4:3 photos.

So yes: some images may be cropped or laid out for the book, but the bigger point is that the page is using mixed examples to compare aspect-ratio effects on composition. That’s why only one image clearly reads as 4:3 while the others do not.

In short, you’re probably not misunderstanding aspect ratio—the page itself is just somewhat confusingly designed or labeled.