Not an expert, but I have read a lot of Harris. And think there is missing something here from how you present his view.

Harris would claim that the "choice" of raising the arm is just as mysterious as the seemingly random alternative movie titles your subconscious if throwing out. Neither is true/full/absolute free will. It just feels like that superficially in the arm example. The final decision on a title, or if you're going to raise your arm, is just as mysterious when you really think about it. It's ALL coming from the darkness of your subconsious mind. It's an illusion of genuine/true/absolute free will.

The reason he mentions how the subconsious is throwing out a few titles from the darkness, is not to define JUST that specific type of scenario as a lack of free will. But more to illustrate an example where everyone can easily notice that they don't have genuine free will. He doesn't think anything is genuinly free even if it feels that way superficially in other scenarios.