I don't understand what his last statement means:

"So please, do not call all functions where the last function call in your source code is a call to itself, tail recursive. A function is tail recursive, if the last operation is a function call to itself."

It reads to me as "Don't call functions that call themselves last tail recursive. A function is tail recursive if it calls itself last."

That's saying the same thing, if my reading of it is right. His oddly-placed commas don't help.