In American English "next best thing" means second best. It is used to suggest an alternative when you can't get what you want. "Don't have Coke, maybe get a Pepsi, it's the next best thing."
"Next big thing" means upcoming good thing.
"Next big thing" means upcoming good thing.
They want something that isn't likely to be misinterpreted, and I've never seen that phrase used to mean "next big thing", only "second best".
Big country though, could be a regional thing.