Matt Levine's explanation of what happened is considerably less sensationalized. Take a look at the second item of his column today [0]. It's too long to quote and doesn't lend itself to an easy excerpt, but here are the facts that he quotes, from Bloomberg [1]:
> A sudden surge in the overnight rate on Treasury repurchase agreements that began on Monday continued Tuesday -- with the rate opening at 7%, according to ICAP. …
> What happened was an unfortunate coincidence -- just as companies were withdrawing cash from money markets to pay corporate tax, a glut of new bonds appeared on the market as the U.S. government sold some $78 billion of 10- and 30-year debt last week.
> With just $24 billion of bonds maturing in the period, this became one of three occasions this year when the imbalance between debt redemption and cash needed to buy new Treasuries exceeded $50 billion.
Again, if those paragraphs don't obviously relate to the overnight lending market, read his column for context.
[0]: https://www.bloomberg.com/opinion/articles/2019-09-17/wework...
[1]: https://www.bloomberg.com/news/articles/2019-09-17/it-starts...
> A sudden surge in the overnight rate on Treasury repurchase agreements that began on Monday continued Tuesday -- with the rate opening at 7%, according to ICAP. …
> What happened was an unfortunate coincidence -- just as companies were withdrawing cash from money markets to pay corporate tax, a glut of new bonds appeared on the market as the U.S. government sold some $78 billion of 10- and 30-year debt last week.
> With just $24 billion of bonds maturing in the period, this became one of three occasions this year when the imbalance between debt redemption and cash needed to buy new Treasuries exceeded $50 billion.
Again, if those paragraphs don't obviously relate to the overnight lending market, read his column for context.
[0]: https://www.bloomberg.com/opinion/articles/2019-09-17/wework...
[1]: https://www.bloomberg.com/news/articles/2019-09-17/it-starts...