It states in no uncertain terms that "always be coding" is wrong. That you should instead spend your time practicing techniques you never use when creating actual software, and that you should also maximize your interview count for salary leverage.
"A lot of what I'm suggesting to do is pretty extreme. A lot of the skills here are not something you learn by doing a standard software engineering job (or get coming out of college). It's especially hard for more senior engineers to do technical interviews since most have limited time due to familial obligations and haven't taken CS 101 for quite some time."
Maybe not secrets, but lessons learned from the current state of the industry. Each one of the points I make is either from a mistake made in an interview I've personally given or received.