Was the pillow itself stained, or just the pillow case? If it was just the pillow case, then I don't get why pillow was replaced. Regardless a pillow case being stained is IMO normal wear and tear. It's put on the pillow partially to help protect the pillow.

As for it being bodily fluids, those are on every sheet regardless if visible. Semen/urine/💩 are all commonly found and perspiration is going to be on every touched sheet. Bleach does wonders! For the rare non-white, there's other disinfectants.