That "spunkiness" may have been internal pain instead, or, the stress of everything may have predisposed him to pick up something contagious at the show, & because he wasn't eating & was the smallest (perhaps weaker?), may not have been able to fight it off. You'll never know, but just that it "happens" sometimes.
Many more snakes survive in captivity than they do in the wild- nature makes shorter work of those with inherent weaknesses, whereas in captivity, the optimal conditions we provide them helps some survive that otherwise would not have. I don't think this breeder was to blame either- not every thing is in the control of the breeder. I'm really glad you're moving forward with another one. Things in life do go wrong sometimes- all we can do is the best we can- it doesn't seem there were any "mistakes" here to learn from- just bad luck. Wishing you MUCH better luck going forward.