Christian said: “The only explanation is that frog attained jhana. It’s pretty interesting if jhana would be possible for animals :) “
I do not think so. However, they can have pitī which is a factors of Jhanas.
There was a story of a disciple who was a dog who followed a paccekabuddha in one of his past lives. When the paccekabuddha reached parinibbānna, the dog died of grief. After his death, he took rebirth, as a Deva. After his existence as a Deva, he was reborn, as a human. He met Lord Gautama Buddha and became an sotāpanna.
His story as sotāpanna
His story as dog.
In both cases of the dog and the frog, we can see that they experienced extreme and contradictory emotions. However, the two ended up in a happy rebirth.