وَالصَّفْرَاوِيُّ قَدْ يَجِدُ الْحُلْوَ مُرًّا
A person described as affected by yellow bile may find sweetness bitter.
The text uses a historical medical explanation for altered taste. The aim is not to assert a modern diagnosis but to show that a person's sensory experience may differ under particular bodily conditions even when the external object remains the same.
Imagine that medication changes someone's sense of taste. The person may truthfully report the altered experience, but this does not establish that the food's external properties have changed for everyone under every condition.
The epistemic lesson is to identify the special cause of the variation instead of treating it as a refutation of sensory knowledge in all normal circumstances.