How did my engine eat itself?

I have a 2007 XC70 that I bought used three years ago. This car has been a dream, never had any issues of any kind and I have taken it to my local mechanic twice a year for the normal maintenance. The mileage is around 113,000 miles. Last week, we loaded up our camping gear and headed into the Yukon for a road trip. Prior to this road trip, we had the oil changed and bought a brand new battery. After driving 200 miles without a hitch, we parked the car at a campground and put our canoes in the river and off we went. While we were on the river, a friend came to pick up the car to stage it for us in another town but she said the car was driving strangely, couldn't get up the hill, revved up to 6000 rpm, and then the "no oil pressure- stop car immediately" light came on. She stopped the car, had it towed to a mechanic, and now the mechanic is saying the engine has a "very loud knock in the lower unit" and we need a new engine. I wasn't driving the car when it happened and I'm not with the car now, but before this happened there didn't seem to be anything wrong at all (no sounds, no smells, no wobbles, no leaks, nothing).

I have several questions: how did this happen? How did this happen so quickly? Is this not a good car to take on a road trip? Is it a terrible mistake to get my oil changed?

Next, where do I get a new engine? If I replace the engine, how do I know this will not happen again?