Why is rest important and what does it have to do with Picasso?

"The second day, a different dealer came by. Picasso hardly looked up. "Fake!" he bellowed.

After the dealer left, I couldn't help myself. "Picasso, why did you say that painting was a fake? I was here, in this studio, last year when I saw you paint it."

Picasso didn't hesitate. He turned to me and said, "I often paint fakes.""

(The full piece is available here.)

Was he talking about staying in the flow and therefore being able to stay authentic?