Because the proposed mechanism has nothing to do with histamine or immune response. Such a K+ channel blocker should hypothetically have the same effect in the vast majority of the general population.
Hypothetically if a person did experience myalgia as a direct result of drinking Earl Grey tea and their proposed mechanism is accurate, the treatment would probably involve K+ channel opener with a lower K_d (higher affinity) than the culprit bergapten, perhaps Diazoxide.