The therapist would probably care little, you are still paying them. Maybe they would even try to see how long it takes you to notice that they already know and just doing it because they keep getting money
As a therapist, I would immediately notice, but would instead use the opportunity to work through their need for attention from strangers and why they use pranks and humor to hide their true emotions. They're still paying me to help them, so I would. "Why do you feel like you need the excuse of a third person to dare going to therapy?"