Why do different codes work to get the secret ending in INSIDE?

So if you got to that point, it means you already got all the orbs. I'm assuming, though, that given your question you don't really know where to get the code from, and only got it from the guides. So let's go back a bit.

Remember how to get orb #5? After you go down the stairs, you'll notice some sounds start to play in the background. Now, one might easily mistake those for just ambient music or something, since the game often makes moments more intense by just adding some ominous sounds to the background... but if you stay there long enough, you'll realize there's a looping pattern going on there. If you've been to the door to the vault where you need to input the code, you'll also notice that the left, up, and right sounds match the ones being played here!

And so there you are: the code comes from a looping sequence, and so it just doesn't matter what the starting point for your sequence is. Both of the codes you mention are actually the same one, just starting from a different point, and looping around to wrap it up in 14 steps (14 which, not by chance, is the total number of orbs/achievements you can get in the game).

I haven't looked into the game, but both the codes you posted have 5 Ups, 5 Rights, and 4 Lefts, and they all have a 3-in-a-row for each direction. (ex: Up, Up, Up)