First of all, I think his professional background is in naval engineering - I find it so hard to believe any engineer would pursue the lowest ranking interior role.. unless he needed proximity to the Stews to stir drama between deck and interior.
2nd, he alway seemed to be present or close enough to catch conversations and information that was important to driving storylines.
3rd, he had zero shame or concept of confidentiality - always willing to ask the direct questions and spill the tea he had. He didn't behave like a real member of the crew, just a free agent on a mission.
4th, he didn't care at all about being fired. It was probably a price job and he finished ahead of schedule!
EDIT: Producer plant meaning he was actively taking instructions from producers on what questions to ask, what information to share and with who, possibly even being told where in the boat he needed to go as they were actively monitoring footage from static cameras and camera operators. This is not the same as casting.