Regardless, in his industry he'll observe trends and could tell you what engines are reliable and which tend to be short-lived.
Granted, he didn't necessarily speak to that in this video, but I recall he's made comments in other vids (the specifics of which I could not readily cite).
You make a really good Point, he most likely gets engines that have failed. A scenario here, a car gets hit in the rear and it is totaled by the Insurance Company. The car had 5000 mile OCI's with Mobil 1, it still runs, why tear it down.
earlier this week I saw a Kia soul try to overtake a slow poke motorist from the burst of black smoke out the exhaust and the immediate failure to pass I am now wondering if something like this had occurred that night.