I believe the ending is ironic, but more because the characters are mistaken in their happiness due to their ignorance of other events. At the end of the story, the storm did indeed pass, and because of this, the characters were very happy. However, if they truly knew the situation in which they were, they wouldn’t be happy at that moment.
At the end of the story, the characters are all happy, but the others are ignorant of the events that happened during the storm. Ironically, Calixta is happy, but it is because of the affair she just engaged in. She returns to her husband and son full of joy but also having betrayed them.
Additionally, Bobinot has purchased shrimp, hoping to bring some joy and something about which they’ll be excited for that evening after the storm, which his wife seems overjoyed at. However, his concern is unwarranted since she has clearly found her own pleasure outside of the relationship. The crux of the irony here seems to be on the ignorance of the other characters’ actions.