I think it’s just the gas cap.
What facts do you have to back up your conclusion?
The O2 sensor is part of the fuel delivery feedback loop.
The gas cap is part of the evaporative emissions control circuit.
These are completely independant systems and the control unit has separate error codes for those systems. IMO, the gas cap causing an O2 sensor error is about as likely as the hub cap. So, I’m interested in your logic…