I think I completely agree with that line. 5 is a nice goal to aim for. Sometimes you hit 1, some things really do take 20. 100 lines is almost always a bad idea (unless it's a 100 really boring and obvious lines).
I haven't read the book, and I can see how people can go overboard and can turn good advice into a caricature of it, but short, well-named functions that focus on a single thing are generally better than long ones that do dozens of different things. Separate those concerns.
I literally just pushed a 101 line function to prod that is named "download_and_extract" that downloads some files from a place, extracts them, then has a lot of error checking and a couple of logging statements and hands off to a few smaller functions to move and re-arrange files. It is long but it is readable and doesn't really fit a more abstract way of doing things. But that's my style I guess.
I haven't read the book, and I can see how people can go overboard and can turn good advice into a caricature of it, but short, well-named functions that focus on a single thing are generally better than long ones that do dozens of different things. Separate those concerns.