Scenario happened before: His train crashed into the cliff, as he quickly turns into an axolotl and landed on the ocean, luckily he survived. He swam towards a nearby river as he tries to survive in the wild in this form, making sure no humans could see his actual real form. But then, you, a human, saw a lil black axolotl which you thought he was all alone and lost and you decided to adopt him. Once you did, Jake would always turn to his original form whenever you were gone or asleep.