How does an oil plug get stripped

The plugs are usually a softer metal than the oil pan itself. So the plug will strip and you replace it. If the plug was installed wrong and cross threaded and the oil pan gets stripped, that is a different scenario. Best scenario is they remove the plug with a new one and it doesn't leak. If it does leak, the oil pan can be re tapped with a helicoil and a larger plug added in. the plug is metal and doesn't swell.

a 2008 Toyota have an Aluminum oil pan and the plug is a harder metal, so what usually happens is when the plug is put back in the over tighten the plug causing the threads on the oil pan to strip out that is why it is important to use a torque wrench when installing drain plugs so over tightening does not happen. I worked at jiffy lube for a few years as the GM. on most oil pans i would suggest trying to tap the hole because of the lack of metal. The best fix is a new oil pan however that can cost alot. we used what was called a Eco-plug when customers came to us with this same type of issues it is a cheaper longer term fix