I wouldn't want to put my decision to continue ten more hours into the hands of someone on board who claims to be a doctor.
".....impugn the identity of the person who attended to the man by stating that he just "claims to be a doctor."
Every time a doctor has been requested on any flight I have been it was always a call for "A medical doctor" I guess to deter PhD individuals from volunteering.
My daughter is a UK hospital "consultant" and previously as a hospital doctor has volunteered when on board.
She has her UK General Medical Council ( GMC) Registration Number and other forms of ID so she can be easily checked out with a call to the ground.