Haha, I understand your doubt... well, as far as I'm aware; where this watch says Mylo Xyloto and the regular version says G-Shock, it would have been pretty hard to successfully get the G-Shock logo removed to then print on it again without destroying it and the detail is pretty precise. Also for what purpose seeing as this Mylo version is not for sale anywhere.
My guess is the watch was specially made for Martin for the album release purely to promote Casio, which has apparently worked wonders as everyone on this forum has noticed it and now wants one! Haha.
Either way, it was pretty battered to begin with, but I prefer wearing a battered custom watch to a sparkling new regular watch with no notable meaning or back story. I wonder what this watch has seen in its life...