Lance had actually been taken prisoner by Uvlavad Kudlak to fight in a war for him. He befriended Clyde Langer and Luke Smith and they confronted Uvlavad. When Uvlavad found out the war was over, Uvlavad returned all the children that hadn't already left his space ship to Earth, including Lance.
Lance's father, Simon Metcalf, was a British Army soldier who had been killed in Iraq. Luke Smith, not knowing this, had coined the nickname "the Corporal" (as in "Lance-Corporal") for him at school. Luke dispensed with the nickname when he realised it was insensitive. (TV: Warriors of Kudlak)