This would be an example of engine hours and airframe hours being out of sync after a lengthy period of operation, where ground testing with engine running is incurred.
Actually if they were in sync before they would still be in sync after precisely because ground running hours were not recorded, not sure what the TBO on these engines would be, but I doubt a few hours of ground running, probably at low idle would be that significant in the big picture - the problem here was totally unrelated to engine wear!