My wife is at 165K and I am 138 K miles. So your mechanics remarks the older prius owners may be damaging their engines are credible excepting the number of 'blown engines' being reported by his client base seems greatly exaggerated to have all occurred in the time span he stated.
It is true that they begin to burn oil and my wife and I both have 08 prius. I now keep a close eye on the oil because I had a close call where the MFD would blink 'PROBLEM ' going around turns and then go off. Apparently that is a pre-cursor to the triangle or the oil can light appearing so I caught it early. That night I checked her oil which was low as well..