They probably called each other by their last names WHILE they were having a kid together…
That’s what I was thinking… but everyone calls him Turk, not just Carla.
My Grandma called my Grandpa “Lars” (his last name was Larson).
Jeff Foxworthy calls his wife by her last (maiden) name which he referrs to as her middle name.
My Great Grandfather was called “Sherm” (last name was Schurman) by his wife… He called her “boss” 
I worked with a teacher who was XXXXX Pierre. His wife called him “Pierre”, although technically she was Mrs. Pierre. His buddies had introduced him as “Pierre”, and that’s how she’d come to know him.