Legendary Pokémon are very rare, but there is a way to make finding them easier. By using Espionage Mode, it is possible to link up with a player who has seen a Pokémon missing from the first player's Pokédex. Professor P will then say that the Phobos Battalion has the Pokémon in the same place that the second player found it, and the Pokémon can now be found. Each player is assigned a rare Pokémon on their Agent Card. However, this cannot be changed, making it extremely difficult to find legendary Pokémon. This mode however, is deactivated once the console reaches a low battery level.
Another way to find rare Pokémon is to challenge Mr. Who, a collector who collects Poké Balls that fall out of the Phobos Battalion's planes. For prize coins, the player can challenge him. The main difference is that there are seven columns rather than five, allowing for more possible combinations. Some Pokémon can only be found by doing well against Mr. Who, such as some legendary Pokémon.
So I guess what that article is saying is that legendaries in this game don't have specific locations, they are just rare.
Source: Bulbapedia
