Justified because he has spent years on an isolated island.
They're used by the Driver in Men of Courage.
Men of Courage manual lampshades it with the following examples, explicitly written: Only the Driver is American and he is removed from the third game. The Green Beret is Irish, the Sniper and Sapper are both English, the Marine is Australian, Natasha is Russian and the Spy and Thief are French. Prior to that, they are only mentioned by job title (Natasha excluded) or nicknames.