Well, maybe. If the UC and NFSW universes differ from the ones in NFSU/NFSU2/NFSMW/NFSC, than sure, that kinda makes sense. But if World is in the same universe as those 4 games, than it makes absolutely no sense.
I could think that if you put Mystery City in the middle of a big archipelago, it could prove that there are hundreds of mystery cities with only one of them is San Juan which is like finding Waldo but instead finding the city.
But if that was Mystery City, then how can you see all of it from a canyon? This makes a mystery to canyon islands near Mystery City but I wonder how the player or any other opponent would got there.