You can scroll out the text (all screens on DF actually) with mousewheel or equivilent to make pages (and text) smaller and save scrolling, beyond a point it becomes too small though to read unless you have exceptionally sharp eyesight and hunching over to read DF text isn't really a good use of your posture. This is a thing on regular DF too, the guide has just manipulated the image to make it more readable in one go by zooming out and putting it into a smaller frame to make it sharper, because a widescreen DF page stretches and distorts the text.
It works like a pseudo zoom out in fortress mode when you want to watch a lot of things happening at once like the paths your inhabitants are taking, your viewpoint hasn't really adjusted but you can look at things further away or "zoom in" close up.
