Milk and lactose
Milk contains no fibre at all, which is why fibre leaflets leave it alone, and why the restriction, when it comes, comes from somewhere else.
Dietary fibre exists only in plants. Animal cells have no cell walls, so milk, cream, butter, cheese and yoghurt contain no fibre whatsoever. Fibre-focused leaflets therefore treat dairy as unrestricted, and several of them actively recommend fortifying with milk powder to keep energy and protein up.
This book leans on that hard. Milk and cream are how most of these recipes stay rich enough to be worth eating when appetite is small. See fortifying.
Where the restriction comes from
A second axis, layered on top. Lactose is the sugar in milk, and it is broken down by an enzyme made in the lining of the small bowel. When that lining is inflamed, by pelvic radiotherapy or by treatment, it temporarily makes less of the enzyme, and undigested lactose then draws water into the bowel and worsens diarrhoea. That has nothing to do with fibre and everything to do with which complication a leaflet was written for.
So radiotherapy advice and advice for after a low anterior resection can both add a lactose restriction that a general low-fibre sheet does not mention. Neither is contradicting the other. They are answering different questions.
What this book does
Uses whole milk, cream, butter and cheese freely, and flags the dishes that are heavily built on milk so you can see them at a glance. Almost all of those work on a lactose-free milk without any other change, because lactose-free milk is ordinary milk with the enzyme already added, and it behaves the same in a sauce or a custard.
Hard cheeses like Cheddar and Parmesan contain very little lactose, and butter almost none, so those usually stay in even when milk comes out.
What you should do
If you are having pelvic radiotherapy, or dealing with urgency and loose stools after a low anterior resection, ask your team whether they want you to cut lactose for a while. If yes, swap to a lactose-free milk rather than to a plant milk, since plant milks carry less protein and some have added fibre. Check the label, which is worth doing anyway.