Honestly I have a lot of sympathy for him. I do think he should have pulled up long before, but think about it: if he had finished the course riding with a broken rein, not many people would have said anything negative, it would have been all about how amazing it was that he finished (like Mark Todd without stirrups). I doubt in the moment he could really think much about it, it was doable so he did it. Or tried to.
When he lost the left rein a second time, I think his body shifting over to catch the rein told the horse to turn, horse locked on to that fence, his body crouched over told horse to go, he thought surely the horse will stop at the wall, and horse thought it was a brush or something to jump into.
And I didn’t see a “temper tantrum” after, I saw a guy who was frustrated with himself. I probably would have been cussing myself out while I got my bearings and got my brain working well enough to find my horse.
Sometimes I wonder if people that villify others for not immediately running to check on the horse have ever had a high adrenaline, high speed fall. I have. Your brain doesn’t function right at first. Even though he didn’t actually fall and hit the ground, it still takes some time for your head to get out of that intense, in-the-zone focus. Not to mention you know in the back of your head that others are catching your horse so for a second you can get your bearings, be upset, then get back to business.