The "Robot" is unable to stand perfectly still, like a machine would, because it is actually a person dressed up in a suit.
When Gilligan and the Skipper spot a man parachuting to the island, they go looking for him. It turns out to be a robot and he has landed in the clearing where the castaways usually congregate. Gilligan, Skipper & Professor continue to search for a man but the robot was right in front of them his parachute spread out behind him. They should have seen the robot right away.
Ginger is wearing a wedding ring in the scene with the robot.
When the Skipper says "...a man works his way up to be the captain of his own ship...", he clearly moves his mouth to the word "poop" instead of "ship".
Bizarrely, the robot is only programmed to build model ships and aircraft carriers, but nothing in between.