This is real life FIFA Career Mode, when you sign Messi, but don't have a number to give him, so you just leave the one the game chose for him.
Surreal.
Btw, I know 30 is not an insignificant number for Leo, but I would've still expected him to maybe choose 19 instead. Although 30 was his first, and since he never wanted to leave anyway, it makes sense to start a new story in a new club with that same first number.