The author doesn't mention where he went on retreat, but there's more than enough information in his post to figure it out. I won't name them, but I will say that they aren't a monastery and aren't part of an established Buddhist tradition. The movement that the retreat centre is affiliated to was established in the late 1960s by a businessman with no monastic training. Bluntly, there are a lot of organisations out there who are accountable to nobody and are teaching stuff that isn't Buddhism, but sorta-kinda looks like Buddhism if you don't know any better.
Actual Buddhist practice is, by and large, considerably less bizarre. Not eating after noon is the sixth of the eight precepts accepted by laypeople during retreats or special days in the Buddhist calendar. The purpose of these precepts is to focus the mind on spiritual matters rather than worldly pleasures; they aren't all that different to the restrictions of Lent, Ramadan or Ta'anit. The overwhelming majority of religious and spiritual traditions make use of some kind of temporary asceticism.
https://en.wikipedia.org/wiki/Eight_precepts
The eight precepts aren't terribly difficult to follow, but they can be a shock to the system, especially if you go from dabbling in meditation to an intensive retreat. More significantly, meditation is much more physically and mentally taxing than you might expect, so an intensive schedule of meditation can be utterly exhausting if you haven't built up a baseline of endurance. It'd be like going straight from jogging in your local park to a desert ultramarathon.
No reputable Buddhist sangha would invite someone who is pretty much a total novice to a ten-day retreat. I'm a fairly experienced meditator and I'm comfortable with sustained and lengthy meditation sessions, but there's absolutely no way I'd go on a retreat of this level of intensity. Novice monks in my tradition wouldn't be expected to follow this kind of schedule, let alone people who had just walked in off the street.
I think there's a problem on both the supply and demand side; dodgy organisations are offering recklessly intensive retreats, but there's also a broader culture of extremism and quick-fixes that drives people to seek Enlightenment In A Week™. A huge amount of diet advice is dangerously unhealthy, because sensible eating is much less appealing than "The Miracle Diet - Get Your Perfect Body In 21 Days". CrossFit practitioners joke about rhabdomyolysis, a potentially fatal symptom of extreme overexertion. I regularly see submissions to HN that brag about extreme "productivity hacks" that involve chronic sleep deprivation or eating pseudo-food substitutes.
Ironically, this all runs directly contrary to one of the core tenets of Buddhist practice - the Middle Way.
https://en.wikipedia.org/wiki/Middle_Way