When a person is injured or knocked unconscious by someone else, they revert to their original (human) form, like what happened to the Queen against Big Mom.
When the hammer is injured, it transforms into a squirrel, so it's possible that it's a squirrel that ate the fruit from the hammer (I think it's a 0.000001% chance).
But since Ragnir is called a weapon, it makes sense that it's a hammer that ate the fruit, and when it was chained, it was in the form of a hammer.
What does this even matter anyway?