It seems like the author is conflating natural dialogue with creativity. You can't give a character much personality in a few lines of text, so Mother-style quirky dialogue (as in the Undertale example) is one way to make your NPCs more memorable despite that constraint, but they definitely won't sound like real people or have much character. "An animal walks another animal on a leash" is a joke, not a character.
The author shows how to turn a short hint into a more fleshed out character interaction, but "personality" is limited to a trait ("brave", "klutzy") or a relationship to the player, and in an effort to convey these traits in just a couple of lines of text, they end up coming off as forced, contrived. Definitely an improvement from the walking hint, but trying to convey a personality in too few lines and having it come off as a caricature, in my opinion, is worse than an underdeveloped character.
The author shows how to turn a short hint into a more fleshed out character interaction, but "personality" is limited to a trait ("brave", "klutzy") or a relationship to the player, and in an effort to convey these traits in just a couple of lines of text, they end up coming off as forced, contrived. Definitely an improvement from the walking hint, but trying to convey a personality in too few lines and having it come off as a caricature, in my opinion, is worse than an underdeveloped character.