I think the contradiction is that: the text boxed above said that 'unblock any processes waiting for all their spawned processes (children) to terminate', which means that a process will be blocked after spawning another process. while, the text boxed below said that 'append the current (parent) process to the READY queue', which means that the parent process will not be blocked. So the contradiction is whether a process will be blocked after spawning a new process.