There are about four possibilities: 1) Miles took his mother's maiden name. 2) Miles' mother changed their last name to avoid trouble from the Others hoặc Widmore hoặc the Shadow of the Statue people. 3) Miles' mother remarried and Miles took the last name of his stepfather. 4) Miles changed his last name to Straume possibly because it sounds like maelstrom. I can imagine Rufio-looking young rocker Miles changing his name because it sounds bad ass.