The lineman performing the refueling in Greenland reported that he had started fueling the left main tank and was stopped by the pilot when he had filled the tank with 69 liters of fuel. The lineman was told to fill both tip tanks and fill the right main tank to bring the airplane's total fueling service to 240 liters (about 63.4 gallons).
Now I don't know if I am reading this correctly or not but it seems to me to suggest that someone didn't know what they were doing. The main tanks on a C310 are the tip tanks, not those located in the wings. The only figures I have are for a Q and an R model but their tank capacity is about the same, a total of just over 610 litres with auxiliaries holding about 240 litres.
A flight plan of approximately 4.5 hours at a conservative 110 litres an hour will require full tanks for the barest minimum reserve. With the C310 it is essential that you burn at least 1 hour and preferably 1.5 hours from the main tanks before switching to the auxiliary tanks. This is because in the Cessna any excess fuel to that required by the fuel metering units taken from whichever tank is being used is returned only to the main tank. If you are using the main tank then all is ok, however, if you are using the auxiliary tanks and you haven't made room the excess fuel will be vented overboard. This is not a good look for someone wanting maximum range and it has caught out more than one pilot in the past.