The term "vaguely-related" is perhaps wrong, but the "it's not one disease" is clearly correct. Just like "viral infection" is not a single disease, going by yo

The term "vaguely-related" is perhaps wrong, but the "it's not one disease" is clearly correct. Just like "viral infection" is not a single disease, going by your own example, but a series of completely different diseases that have one particular mechanism in common.