Unless I missed something I don't get why Sawyer would have even though that.
Sawyer believed that because in a previous episode, I forget which, he asked Smokey why he couldn't just fly over the water to Widmore's camp instead of having to take a boat. Smokey made it clear that he couldn't do that.
Sawyer foolishly put two and two together and came up with five and Smokey allowed him to make this mistake.