Whenever a vehicle is overturned it usually means the vehicle went off the road and toppled over halfway and not completely rolled.
But sometimes police will put in the reports that the vehicle overturned when it rolled at least once so when a vehicle overturns it could be that the vehicle overturned over onto it's top and is upside down.
Most times whenever I've heard of a vehicle being overturned the vehicle was just rolled over onto it's side and hadn't completely rolled over.
It's very easy to overturn your vehicle especially if you're traveling at a high rate of speed down a dirt road and then try to swerve to prevent hitting a deer.
That happened to a friend of mine when he was a teenager.
He was driving his truck down a dirt road and speeding then a deer jumped out in front of him and he tried to swerve on the dirt road and lost control of the vehicle and it ended up in a field overturned.
He only got a few scratches and the truck barely suffered any damage but it can turn out worse.