It's really important to follow the sources when you see something like this quoted. The article you link to is not an actual study in which people were given Vitamin D. It is a review article, and the specific sentence you quote references an article by Michael Holick, who then references two other articles. One of those articles is just a review, not citing new evidence.

The one piece of evidence that these are all referring back to is a small study done in men in high latitudes in winter, when skin production of Vitamin D is decreased. It consisted of a small number of patients who were randomized to receive different amounts of Vitamin D, so only a small number actually got 10,000 units a day, the highest dose. And this was over a period of just 5 months. You can read the article here: https://pubmed.ncbi.nlm.nih.gov/12499343/

Note that the highest dose in this study was 10,000 units a day, which I would agree can be safe for some people over a short period of time. But it was not necessary in this study to attain goal Vitamin D levels, and over time that dose can definitely cause problems.

Also, where is the 50,000 to 100,000 unit evidence coming from? I'm not sure actually, since there are no human studies looking at that dose. This may be a "theoretical" dose based on studies in other animals, or a false extrapolation based on human studies.

Also, Michael Holick is a controversial figure. A lot of the articles pushing high doses of Vitamin D lead back to him. Please read this NY Times article for a great summary of his issues: https://www.nytimes.com/2018/08/18/business/vitamin-d-michae...