And you are both wrong. If you ever managed to deepthroat a stallion you would probably die. At the least you would be in the ICU for months.
The guy that died didn't die from the force of the stallion's orgasm, he died from the same thing that would kill you if you tried to deepthroat one. Stallions flare. Horses have big babies so mares have big vaginas. To keep his precious seed from just running out on the ground, the stallion's glans expands (flares) to fill the mare's vagina. A mini might be grapefruit sized. An average horse would probably be cantaloupe sized. And a big boy might be bigger than your head.
Having something suddenly (and it happens fast) expand to that size inside your throat or colon will definitely break things unless you have spent years training for it. And stallions, just like every other male creature on the planet, have an instinct to put it in as deep as it will go at the moment of orgasm. If you aren't prepared for that, you are going to be hurt. And that is something to worry about.