If he was playing online, randomizer is a version of the game on an emulator (so automatically a ROM file) that completely randomizes:
   - Starter Pokemon & their items
   - Wild Pokemon, including event Pokemon
   - All other in-game Pokemon, including trades and prizes
   - Trainer Pokemon
   - Trainer titles (like 'Lass' or 'Pokemaniac')
   - Items found on the map, including hidden items
   - TM attacks
   - Pokemon-TM compatability
   - Pokemon themselves, including types, stats, palettes, abilities,
       wild hold items, and movesets
   - Redefining certain evolutions so trading is not required
   - Changing some core game things, like stacking TMs in groups of 90,
       starting with the National Pokedex, or modifying store stocks.
Source
Hope I helped!