No, you do not have to prove how the product defect occurs to win a products liability claim. The product manufacturer has strict liability when they create products that are unsafe. You must be able to show what the defect is and how it hurt you, but you don’t have to prove why the defect occurred.
You don’t have to show why a manufacturing mistake occurred by digging into the details of the production process. Instead, you have to show only that the product is defective. Negligence is not part of a products liability claim, but you may still assert negligence as a separate claim in addition to products liability.