I don't see that sentence anywhere in the guide. Where did you find it?
The actual quote was this:
"Em dashes are great for inserting clarifying details, quick shifts, or sharp asides—without breaking the sentence. I love them. When used well, they add rhythm and emphasis. They help writing flow the way people actually talk."
Deciding you like em dashes— and writing a blog post saying so—because an AI told you they were good for human writers—is funny behavior—even if "you" weren't LLM output masquerading as an author.
It's very generous of you to assume a "human writer" wrote that blog post—is it not?