Head trauma is not always visible right away. The brain swelling needs time to set in. Only time will tell and it can takes weeks to heal. I hope your duck will recover fast.
People with brain injuries very often seem to be fine. Hours later they start with a headache and become disoriented...
That points to head injury. He may have hit his head hard either in the tub or while jumping out. There is nothing you can do, but give it time and hope that it will improve. A good trick is to close the shower curtain so they have a visual barrier and will not try to jump out.