The big question here is, if you hadn't seen that you would have spiked a King on the river, or if nothing had come up at all, would you still be questioning that fold??? If not, then your just being results oriented which will just get you in trouble in future games if your thinking ohh that one time I folded and would have won on the river. That's when you end up shoving into Aces or Kings. There's nothing wrong with making a good fold, even if it turns out you would have gotten LUCKY. You clearly had enough behind to still play in the tourney, because I doubt you'd fold there if it meant crippling your stack. So way to save it for another opportunity with a lot less risk.