Comment by Cessika on A Returner's Magic Should Be Special - Chapter 45

@Cessika bro if i say that im from future would u belive me lol

@jai gamer that's a silly way to put it if you take the time to think about it. We don't know each other so ofc not. 
But they've established a strong conexion already and they've known each other for decades. Desir has all the knowledge he'd need about him to show they were actually friends, as well as knowledge about the future he can use to support his words. Totally different from your scenario