My reading of the rules seems to suggest they made a mistake not allowing you into the F lounge.
oneworld lounge access for First Class or Business Class travellers
Indulge yourself before departure in a wider range of airport lounges when you fly First Class or Business Class with a oneworld member airline.
Customers flying First or Business Class have access to the equivalent class of lounge regardless of their frequent flyer status. First Class passengers may have access to a Business Class or frequent flyer lounge if a First Class lounge is not available.
First Class passengers may be accompanied by one guest travelling on a flight operated and marketed by a oneworld airline.
Customers flying in Economy class on a domestic or intra-European segment to connect to or from a oneworld longhaul First or Business Class flight can also use the lounge applicable to the class in which they are travelling on the longhaul segment.