Gulen's "FETO" followers are Turks. It's a large Islamic faction inside Turkey that has been working to overthrow Erdogan for a long time. Tensions were rising for several years until finally they tried force and violence via the Coup. Foreign "agents" are the connections FETO established with NATO. We do not know the extent of who corroborated or by how much. It seems reasonable to assume FETO may have gotten in close and friendly with NATO to help assist them with legitimacy after the Coup.
It's a world of difference if FETO's relationship with NATO was on a personal level with a few key members stationed inside Turkey, or if there was any official support or legitimacy provided. It's possible General Campbell and/or NATO is only guilty by association.
Gulen used to be buddies w/ Erdogan before some falling out. It's a civil war type deal, only jingoism just happens to be a more effective tool/weapon for Erdogan to employ on folks whom that's effective on.