Rly depends on your relationship with him tho. If you guys are in a relationship, maybe he wants to prove that he has no secret and you can open his phone and go through his dms or something? If not, maybe he just wants someone to hold his phone for him. Either way, don't overthink. Hope this helps!
When doing the X method, the numbers on the sides(3 and 6) have to add up to the number on the bottom (9) and multiply to get the number on the top(18)