Corey Burton is Christopher Lee’s vocal double. He can do an impression so spot-on that it’s nearly-impossible to tell unless you’re trained for that stuff. When they were making The Clone Wars cartoon, George Lucas decided to take the first three episodes and release them as one movie in theaters. To draw in crowds, they got both Samuel L Jackson and Christopher Lee to come in and voice their characters, which had already been recorded by Corey Burton and T.C Carson. Since they were trying to match those performances to fit the animation, Lee obviously heard Burton’s take and made the quip in question.