This is a very low effort, unsourced listicle, that is probably wrong on several points. Disregarding that, I was more curious about how this particular person managed to get hospitalized.

True enough, but it does outline the potential nutritional shortfalls of extreme food regimes, most of which I was aware of. It seemed to sum up most of the obvious shortfalls - I was only passingly interested and this was a low hanging answer. I have seen numerous extreme diets. Many of which are OK in the short term - but not in the longer term. Unless the OP replies - I have no idea in detail what befell him?

Perforated bowel.

How did you get to that point? Diverticulitis?

Constipation believe it or not.

opiate linked? Opiates often paralyze peristalsis = gut walls die and perforate.

Nope I don't take any drugs of any kind. Low fibre in keto diet caused an obstruction and perforation.

Keto can definitely cause constipation under some circumstances, but I'd be dubious about linking it to fibre. Fibre also doesn't count towards carbs, so it's not something that you can't have.