first into a vertical hole in front of him. Think of the section he was in like a T, and the top of the T being where he was before making his fatal error, with the tail of the t, being the hole, a hole so tight he would have had to inhale to make himself skinnier, to fit, and shimmy and wriggle his body forward like a snake while upside down to progress through the vertical hole, until he realized that said hole was not a through passage, but a dead end. And at that point he was stuck upside down in the caving equivalent of a Chinese finger trap.

Even if you know a particular section of cave, it's still recommended to avoid descending steep chutes face first, to always go feet first. If it's an unexplored section of cave, or somewhere you are unfamiliar with this is doubly true.