By asking Winner whether or not they think he can figure out the passcode by seeing the totaled number or from seeing the 0, he removes the possibility that the calculator could show the number that Seungyoon entered in as his passcode and creates a mental distraction focusing on the 2 irrelevant numbers.
Wondering if Mr. Magician ever had the phone facing him before locking it (to retrieve the passcode), why it was locked displaying 0 but a random number displayed after being unlocked and why that number fades to 0.