Cloned games are games that use most or all of a potentially stolen source,to then be claimed as the creators own production. Even if you change a few names, and what have you, it's still a clone. Unauthorised forks, are game derivatives that use, or are based on, sources that were not ment for the public eye.
The issue with both of those types of games is that, if you are just going to claim work from others as your own, your image suffers, and when you're not the one actually writing the code, you might leave unfixed bugs and or exploits on the table. I'm not saying that if you write the code yourself, you're not perfect, so issues and exploits or so could rise, but at least you'd know where to look for them if you see the results. Also, it's just not right on so many levels to steal stuff, if game code would be a car, would any cloner still be as willing to grab it for a joyride?
As was said before: sounds are a bit of a different matter, unless you can actually call yourself the official owner of certain libraries and what not, or when you use stuff from free sounds and or other free to use libraries. If you don't have the library, or don't use sounds from freesounds, but rather go and collect sounds from other games, as well as songs or anything else, you're landing in darker territory.