Factual error: The alligator mentions wanting a Bananas Foster. This dessert was invented in 1951 but this movie takes place in 1926.
Other mistake: When the old woman is cooking gumbo in a large bathtub, it's shown boiling and really hot. Yet the two frogs can sit right on the rim of the bathtub inches above the boiling food in a non insulated tub without getting burned or even hot.
Answer: Naveen told Tiana about his plan to marry Lottie once they arrived in the swamp. After revealing that he's been cut off by his parents, he explains that he plans to regain his wealth by marrying her so that he'll inherit her father's prosperity.