I started thinking this over in the ax sub, but I figured it fit better here.
On the topic of guys tapping out. I work as an activity instructor doing adventure activities, high-ropes courses, canoeing, hiking, that kind of stuff. Mostly with kids, but adults come along as well, often teachers, sometimes parents, and I've done some work with the general public. Not extreme sports by any means, but stuff that does scare people (and is designed to).
I've seen a lot of tough guys crumple on a little zipline, even though they are in a harness, and on a rig that is rated and easily capable of carrying tonnes of weight. I've seen guys lock up six feet off the ground on a climbing wall, or start to hyperventilate while standing on a solid log 20 feet up. Again, with harnesses, ropes and supervision, safer than crossing a street. Its not uncommon to get this sort of reaction after the person has done an activity that is objectively more difficult or frightening.
None of them expected it, and I think that's the key here. You can never tell whats going to set off that adrenaline rush, and when its something that feels little or silly, it can really break people's confidence in themselves. A lot of people go through a lot not feeling fear, or when they do, its a thing they feel is valid, or somehow worth their feelings. So when a little bear gets your heart racing and you think that you should have just kept cool, it can really disrupt everything, make you question yourself, and ultimately if its not a mindset you have practiced, it can be really hard to get back from there. I tell people all the time that fear is a natural thing, but Frank Herbert was right, Fear is the mind-killer, you have to be familiar with it to defeat it.
I didn't see the episode, so I'm going second hand here, but I can see how it could easily happen to someone who was very confident. Fear and self-confidence are always in tension, fear as a natural reaction that keeps you careful, keeps you safe, but needs to be managed, and self-confidence which when backed up with skills and experiences doesn't get tested often. But when that Fear goes to 11 and doesn't gel with the self-confidence, the whole thing can break wide open. That's the worst place to be, because as I said, if you can't use your self-confidence to bring yourself back to a stable mindset, and you question your abilities to function, its not hard to talk yourself into leaving. I'm sure he regrets it, but that's life.
While we all know that fear has a fairly large physiological component, adrenaline can cause all sorts of reactions, its not always the same reaction every time. Those reactions can also start a feedback loop on the psychological side which increases the stress level. I can't count the number of times I've asked a kid what they are afraid of and the response is not falling, or equipment failure. Its that they can't catch a full breath, or stop their legs from shaking, or that their hands no longer work right. The only reason I get that from kids, is that they tell the truth, adults hide it, or don't try.
So you have someone who spends a day, maybe more, amped right up. Gear has been checked a hundred times, gonna be on TV, maybe the flight isn't so smooth, baby crying two rows back. Stress level is high. Gets to the site hears the boat or plane leaving, fear is there, but normal, maybe a bit up because its not home turf. There's lots to do, so no relaxation time. Decisions to make, each one takes energy. Thinking about priorities, trying to remember everything about the cameras, getting set up. Then the bears show up and spook him just a little. But maybe he's more tired than he thinks, and the reaction is stronger than normal. Confidence gets shaken and in that high stress environment, its not hard for me to see how it happens. This isn't some camp-out in the back yard, the stakes are high, some people feel that stress more than others. Stress, fear and excitement are all sides to the same die. Given time, or in a situation with no exit, he very well may have been able to get past it, and survive, there is no way to know. Because of the way I work and the training I have, I always give my clients an exit, sometime I even make them take it, as the alternative to survival is complete shut-down and you get into trauma territory, and there is no way to guess which way it will go.
TL;DR:
Its all armchair quarterbacking from here, but before anyone disparages folks too much, Fear is impossible to quantify and there is no way to know how or why someone will react. It has nothing to do with mental strength or skills or gear, sometimes circumstances come together that are just too much.