Technically, there's no reason for aliens to refer to earth by its name as its only the name humans gave it. They have their own naming pattern for celestial bodies. Look at it this way, Americans say Japan, but its real name is Nihon. The name 'Japan' is just a botched translation, like Spain from Espana, or the way Native Americans are called Indians because Columbus can't judge distances. Better example, in Edgar Rice Burroughs' Barsoom saga, Barsoom is the 'martian' name for mars and its people, and barsoomians refer to earth as 'jasoom' and venus as 'vasoom.' It's the same way with his Carson Napier series, where venus is called amtor by its inhabitants.
Point is, regardless of why we call it earth or how we arrived at that consensus, we've no reason to assume extraterrestrial visitors will use that name.