Customer Service Rep, I guess. Whatever the ins and outs of this (which seems to have rapidly and un-necessarily spiralled out of control), the 'Captain' would not have been allowed to 'load' either the man or his bags in a UK airline. Ground staff in the UK generally are responsible for what goes onto an aircraft, while a Captain can decide always decide what comes off.
Assuming that in the UAL US world a Captain can allow a 'non-pax' to board AND over-ride security of baggage screening then the CSR needs hanging by the ***** - alternatively, the Captain!
What are 'OMC issues' please?