Auntie and Uncle?

Not terrible. I've seen worse crap. But, I could not figure out why the guy would call his girlfriend's parents by Auntie and Uncle?!! Is that some Indian thing? The first time the girlfriend wasn't present, so I thought maybe he actually IS their nephew, and the parents were simply setting up the relationship the whole time. But, on the next occasion, it was right in front of the Pallavi, and no one batted an eye, like it was the most normal thing ever. I'm just confused, anyone?