This screwdriver hides a mini surprise
When we are children, we want to get older because we think grownups have figured life all out. Then as we become adults, we realize they know nothing; they are the same kids they once were, disguised as mature people. Nonetheless, grown people occasionally reveal their inner child.
This big screwdriver must have fallen and broken, and when it did, it revealed a tinier one that was hidden inside. Someone must have made a bigger handgrip to make it look different or easier to handle, but the tool essence was the same all along.