Maybe the owner ran the milage up?
It is certainly possible — and the more proud the owner, I suppose, the more likely. My guess is that if it had slanted windows it may well have been a highway bus. Let’s say it were a 1955 model and was retired in 1985, 5 million miles would be under 200,000 miles a year. That’s in keeping with the miles run by a fleet operator, but fleet operators tend to have a lot of one kind of bus and get rid of their remaining few when it no longer makes sense to keep parts and tools for just a few of those buses. So it could go either way.
