I think that that was great marketing, and that they chose a car with a very durable powertrain. That 2.5 liter straight six was an amazingly long lived engine if not overheated. I know of many people who passed the 250k mark on the original auto trannies - at least one with only one ATF change. If I wanted to prove my product, be it fan belts or engine oil, that would have been the perfect platform. As long as it wasn't an A/C component or power window part. . .
The test would not have been quite so impressive if they had used a toyota corolla, which also would have gone the distance with no problem.
It would be interesting to know if any OE parts failed during the test; alternator, battery, bearings, etc. We know they don't normally last 1,000,000 miles - but might in those perfect conditions.