two reasons. first, because of the historical animosity between ms and linux. second, because the contributions have appeared high in some site's "ranking" of contributions to linux 3.0. part of the article explains (poorly) that this is because the particular ranking was by number of commits, rather than significance (or number of lines changed). this isn't a criticism of the commits (linux prefers many small changes to one large one), but rather the ranking method used, which misleadingly implied that ms was making "major" contributions to linux.
so the whole conversation is addressing a discussion elsewhere that is based on those two points: ms and linux are traditionally "enemies"; "ms" was misleadingly represented as making major contributions to linux 3.