Well, you see, this is where I differ with most of you basement dwellers.
I don't think any talented fighter would actually quit after their first KO/TKO loss. No matter what they say during the aftermath.
I'd say it's got more to do with the immediate "shock" of not being able to avoid the inevitable. Because the fighter in question had done so in all his previous fights (18 of them). It's kinda easy then to start thinking you're very close to reach greatness, when not even Jon Jones could make you look like a bad fighter in there.
But that's the thing, I don't think that mindset is still there at this point. If Gustafsson would be knocked out, he would be more prepared for it this time. It wouldn't hit him as hard mentally at this stage, as it did when it was the very first time.