I've heard that whether or not a pokemon is shiny in Gold/Silver is determined by its IVs but there is also the red Gyarados which is always shiny. Now does this Gyarados have the same "good" IVs that every other shiny have in 2nd gen or is it a let's say hard coded shiny whose IV are just as random as with every other pokemon?
In Gen II, shiny Pokémon are determined by IVs:
In Generation II, Shininess is determined by the IVs of a Pokémon. If a Pokémon's Speed, Defense, and Special IVs are all 10, and its Attack IV is 2, 3, 6, 7, 10, 11, 14 or 15, it will be Shiny.
I can't find anything to confirm it, but I'd assume that the Red Gyarados has fixed IVs, as there's no special shiny "flag" in the Gen II games.
There's some evidence to support this assumption - not only does the Red Gyarados retain its colour when traded back to Gen I, but transferring its IVs to another Pokemon (via the Shiny Ditto Glitch) also leads to that Pokemon becoming shiny.
As for whether or not the Red Gyarados has "good" stats in Gen II, T as Arperum pointed out, flat IVs of 10 with a possibility of a high attack place it firmly into "slightly above average" territory.