"Pilot" in PIO may be Autopilot too, as we see it in the KC-135R dutch roll report when the captain tried to stop it with A/P. The notion of "fault" is of no use in science. We are concerned by cause.
The human is a variable gain device when it comes to aircraft control systems.
For some type of input, you can get either a large or a small output and that output can have further modification as to phase angle or even anticipation of a signal.
The autopilot is a machine that is constrained by its construction and design to create a certain type of output for a particular input. Normally an oscillation involving an autopilot is not considered to be a PIO. As I understand the KC-135R accident however, the presence of human feet on the rudder pedals caused additional inputs to the system that resulted in an increasing Dutch Roll oscillation. If my understanding is correct, then that would be a PIO under the newer PIO definitions.