In Toy Story 2 In a dramatic scene  , zurg reveals that he is buzz's father, which is an obvious homage to the iconic empire strikes back scene.

But how did Zurg know he is Buzz's father. I mean the only way he could have known that is if it was written on the box which it obviously wasn't.

I ask for apologies if the answer somehow contains Lightyear(2022) since I have not seen that movie.

In Toy Story 2, in a dramatic scene, Zurg reveals that

he is Buzz's father, in an obvious homage to the iconic Empire Strikes Back scene.

But how did Zurg know this? The only way he could have known that is if it was written on the box, which it obviously wasn't.