The explanation is completely incorrect. The outer invocation of `yes` is never actually started. The reason is because the inner invocation is being used as an argument to the outer invocation, which means bash needs to know the entire output of the inner invocation before it even starts the outer invocation.

Instead, all you're seeing is bash thrashing as it tries desperately to capture all the output of `yes no` in-memory.

I expect you'd see the exact same behavior with echo `yes no`.

Now if you really want to screw over your machine, the classic bash fork bomb is

     :(){ :|:& };: