It’s different in Disney World than it is is in Disneyland.
In Disneyland, they have New Orleans Square which is where Haunted Mansion is (thus it’s New Orleans theming). Next to that is Critter Country (which is where Splash Mountain & Country Bears jamboree are), and then in the opposite direction, on the other side of the pond / lake, is Frontierland (which is where Big Thunder Mountain is). These are all technically separately themed areas of the park.
So in Disneyland I’m pretty sure they’re going to be retheming Critter Country & making it like an extension to New Orleans Square. Which then the Princess & the Frog ride fits thematically.
In Disneyworld Magic Kingdom, there is no New Orleans Square or Critter Country. Haunted Mansion is part of “Liberty Square” (which doesn’t exist at Disneyland), and Splash Mnt is part of Frontierland, despite it being a bit of a theming mismatch. They just didn’t have anywhere else to put it.
Edit: also worth noting that at Disneyland, PotC is part of New Orleans Square, not Adventureland, hence why the ride starts off floating through a bayou.