The thing about race weekends is that you normally don't just get one race, you get a lot of little support races. One of those tends to be a "Legends" race, where heroes of years past take some laps around the track. It's supposed to be nice and congenial. Until the cars get destroyed.
The Group C racers heading down the straight weren't exactly tearing along at 230 MPH, like they would've been in their heyday, but they're still pumping out something over 600 horsepower in a package that weighs incredibly little. Add a little bit of rain, and you've got a recipe for massive snap oversteer.
One thing leads to another, and suddenly you're fishing out two very expensive historic works of art from the barriers, and you've got two incredibly expensive repair bills.