2010 Prius 100,000 miles engine blew

Hello, on Saturday I was getting on the freeway and heard a loud pop. My car started vibrating/shaking, I saw a "low engine oil pressure" light come on, and I noticed the back of my car was smoking white. I pulled over immediately and turned off the car. There was a giant trail of oil behind it too. Oil was pouring out from under the front of the car. I've never had anything like this happen before.

I had it towed to the Toyota dealership I do my annual oil changes at. I read online where people had this happen because their oil pan/filter/plug fell out and oil poured out everywhere and caused damage. I didn't bring this up to the dealer, I just had them inspect it and no mention of oil was brought up. My car has never leaked or burned oil before. There really have been no problems with it since I bought it in 2017.

They told me "#4 cylinder head gasket blew causing water into motor and exploded #4 cylinder put 2 holes in engine block." They said it would be $7,000 total to replace it. $4,000 for a used engine with A LOT more miles (150,000!) than my car currently has, and the rest is labor.

I don't know what to do. That is a very expensive repair and I never thought my engine would explode with only 100,000 miles. Can someone please explain what exactly happened and why this happened? Any post I read has cars with more than double my miles needing their engine replaced...