I Googled around a lot but came across only 1 such example where some guy tried combinations (permutations?) on his PS2 controller. But that does not give me the reason how the ones on PC are found.
So, does Rockstar release them or are they just present in the game such that game programmers can open and see while modding or something else?
Best Answer
There are multiple ways a cheat can be found for a game.
The developer can send the information to a website or magazine for "exclusive rights" to some cheats and tricks - this was largely used in the 90s;
The game can be datamined, and as such, getting the secrets in the code revealed by the dataminers;
They can be found randomly, as you said on your question, a player can try combinations until something works.
There's no way we can guess how it worked for the specific situation of GTA, but we can try to have an idea from those possibilities.