How is he over generalizing?

It's just a very simple fact that 90% of the bootcamp grads can't program their way out of a paper bag. In fact, most self-trained programmers are vastly better than even the best bootcamp graduates.

The problem with bootcamp grads is that they don't know what they don't know. And they don't know a lot. Undoubtedly some of them will turn out to be great programmers, but not after 3 months. Or even 6. Or even a year.