That's the key word, "promise". There is no way to get perfect IVs without RNG outside of being one of the luckiest people in the world of Pokemon. While possible, it is highly highly highly unlikely, and that's where RNG comes in. It allows you to search your game for a specific time and ingame frame to hit which allows you to obtain flawless Pokemon. This is due to Pokemon using a pseudo random number generator to determine a Pokemon's IVs, Nature, and so on. RNG just allows you to use a program coded with the ability to decode all that complicated math nonsense allowing you to hit that one in a million chance every time if you do it right so to speak.
Er, I hope that wasn't too convoluted.