That will happen often if you interrupt villagers after they kiss. The "outcome" is determined at the time you hear the kissing sound (check the village population to see if it increased or not). The trip to the hut is there to add ambience to the game, but is not necessary for producing baby villagers. When you interrupt that trip, you essentially cause the game to immediately display the baby that was produced at the time of the kiss.
SPOILER:
Lol. Thank you for explaining that. I had that happen IN the lagoon, and thought that the lagoon influenced them (I had tried to pull them apart to prevent breeding) because the lagoon has those magical properties and such, and she walked out, and there's a baby in her arms. I thought, "OH, ...." you fill in the blank, lol.