I agree, the first part is guessing and reading the celebrities. For instance he pretty clearly was giving the shirt to Simon before he saw that there wasn't enough reaction.
For the second part, I thought it through and decided he knew he was going to write "No," and must have used that time, his only time holding the pen, to draw the other pictures which he slipped into the bag at the end. The only problem is it sure looks like drew the word No, and he didn't keep anything in his hands to later slip into the bag.
Evaluation: true magic!