Why'd they laugh?

Naomi squirmed in her seat as dad drove our way to another meething in FE. "Oh no, it's coming," she mumbled. "What?" Paul looked up from his DS. "Oh, Woodrose."

I glanced out just in time to see Woodrose drift by our window. Then I heard the words escape my mouth before really realizing it, "I used to study there."

"Oh, I get it," Paul laughed. Naomi joined in. I don't really understand why they laughed, though.