[deniska]

Yes and no.

Modding a game means that you have a specific starting point, the original game, which you are probably a fan of. And you may want your creation to be a part of this original world, share some (or most) of gameplay elements, design elements, story elements etc.

People modded Half-Life not only because modding Half-Life was somewhat easier than making an FPS game from scratch, but also because they wanted to explore the original story from another angle, or they liked how engine feels to play, or for whatever other reason wanted a starting point to be a complete game. Kind of the original asset store: the assets of the game you are modding.