It's not anything you did, it's a chemical reaction that has to do with the pleather breaking down. Possibly because it is reacting to something it touched at some point and that basically sort of just made it start going rotten. Or possibly it was just a bad batch of pleather. I had exactly the same thing happen with a DID German Coat I very recently got from Monkeydepot (which they refunded right away when I told them about it). As soon as I took it out of the little ziplock it was in, I could see it was crumbling and peeling and in the days since it has gotten a lot worse possibly because the air is making it break down faster -- which looking at your pictures seems to be what is happening with your jacket.
Really, I don't think there is really anything you can do about it except wait for the new jacket -- which will probably be fine. I've got a ton of "leather" jackets I've bought for my 1/6 dudes over the years and this is the first one that's ever gone rotton on me, so it's not that common an occurrence and I think we just both had bad luck.