Methane is a far less volatile than jet fuel. The energy needed to ignite methane is quite large. I’m serious as to what the risk of ignition could possibly be during refueling.
Methane, for the win.
Of course, throw in some other factors, actual concentration of the methane. One bowel's worth of methane in a small compartment mixed with a couple of cubic feet of air, of which only ~20% is O2, compared to a steady supply of potentially evaporating kerosene out in the open...