How Do People Get Those Level 100 Lugias/mews On Their Pokemon Diamond?

Their Pokémon are hacked? My friends can see people on the Nintendo Wifi with a level of 100 lugia and IM sitting here wondering if this is possible. I even saw someone giving someone else a level 100 Dialga and say “its good, I have a box full of them, badly you free.” How can both Dialga and whose mind giving them out?

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How Do People Get Those Level 100 Lugias/mews On Their Pokemon Diamond?