I’m not sure what medal that is but I doubt it is an iron cross. Why would a British POW have a german medal?
For the same reason Dad brought home a nice collection of German WWII medals from Europe. He took them away from the losers. Also, the guy just walked back from German captivity. I don't think he would have been wearing that medal when he was captured. Just some conjecture on my part, though We'd have to ask the bloke about it.