Read this excerpt from Holes. Stanley’s great-great-grandfather was named Elya Yelnats. He was born in Latvia. When he was fifteen years old he fell in love with Myra Menke.

(He didn’t know he was Stanley’s great-great-grandfather.)

Myra Menke was fourteen. She would turn fifteen in two months, at which time her father had decided she should be married.

Why does Sachar include the line “He didn’t know he was Stanley’s great-great-grandfather” in this flashback?

It makes it clear that Stanley has never met or heard of his great-great-grandfather.
It explains to the reader that Elya was indeed Stanley’s great-great-grandfather.
It is a funny way of pointing out that Stanley and Elya are clearly not living at the same time.
It is a silly way of letting the reader know that Elya and Stanley are not really related to each other.