You're skipping a very important detail in all of this.
The gender.
A sick man deserves contempt, a sick woman deserves attention and caring. Which explains why most men insist they're fine, even when at the brink of death, while women are incapacitated with the slightest headache.
In my experience, women have a tendency of succumbing to periodic ill-feeling. All of it subconscious. This brings the attention of men and family. That constant and consistent caring is habit forming and serves her well in the future when she becomes genuinely sick (or pregnant). There's your evolutionary justification.
This seems like an extreme example of the above. Probably a high status female overdid it and the rest of the females were just mimicking her behavior, all of it subconsciously. While human beings are drawn to certain behaviors instinctively, the nuts and bolts of the behavior is learned and passed down culturally. In other words, women may have a predilection toward periodic ill-feeling, but in what manner they express it is up to them ... or in this case, up to the high-status female.