Well the only difference between Porting and Making is that when you are the original developer of a game you also make all the assets (textures, sounds, models, etc). However when you port a game you generally have to develop the game's engine from the ground up to work on the other platform. Basically Bungie made a Mac and Linux game, then Rockstar built a PS2 version of it. The point is still the same, Bungie didn't touch or have anything to do with the PS2 port of Oni, outside of greenlighting Rockstar to port it.