Note that the author is the head of Sequoia Capital. "Sequoia, notably, also counts the highest number of private, billion-dollar ‘unicorns’ of any investor today and consistently finds itself in the largest tech startup exits."[1] If the head of the VC firm financing the largest number of "unicorns" says publicly that many of the "unicorns" are subprime, it's time to pay attention.

[1] https://www.cbinsights.com/blog/sequoia-capital-teardown/