Pork sausage - difference in food guidelines
The StillTasty link you give for the sausages is for all types of fresh, raw sausages, not just pork. That's why it's labeled "SAUSAGES (INCLUDING PORK, BEEF, CHICKEN OR TURKEY) — FRESH, RAW".

Most likely, they're getting the 1–2-day limit from the chicken sausages (which are likely to have a higher initial bacteria load than pork or beef). Note that they give the same 1–2-day limit for raw ground chicken.

That said, if the manufacturer gives you specific advice, it overrides the general advice from sites like StillTasty. They know their specific product. Their specific formulation probably includes things (salt, acids, preservatives, various spices) which slow bacterial growth, thus keeping it good longer.