That is terrible, but I think you need to cut yourself some slack. While there is a connection between cribbing and colic, I am doubtful that a turned out retired horse who probably only cribbed briefly when confined did enough damage to cause the colic.
FWIW, I don't believe horses "learn" to crib from other horses. I think it's much more likely your gelding started to crib at that show from the strees and tension of the show environment and being stalled 24/7.
Years and years ago, we had a very fancy conformation prospect sent to us for breaking and training. When put up in a stall for half the day, she immediately started to crib out of boredom. This was *huge*; potentially destroying a lot of her value and her show career. We had to hot wire all the surfaces in her stall. I hated it. If she had been mine, I would have turned her out and brought her in to work and turned her back out. But she was supposed a high dollar, hot housed show horse, and cribbing wasn't an option, and neither was all day turn out.
The hot wire worked. But I still hated it.