hello and welcome to HCM forum,
The information provided by you is not complete and ,i cannot actually rule out the diagnosis, but i can assure you that it is not at all related to the his medical history.
what i can say is that the filling or the metal crown placed after the root canal treatment
might be high at certain points, which is causing pain in the temple region and may even give a metallic taste
i would like to request you to visit the dentist
who performed his root canal treatment, and get the tooth re-checked to make sure everything is in place.
i wish you good health.