They weren't wrong. Its core business in what is still a viable-enough sector collapsed. Or if it were truly well-managed, running an ISP and a retailer should have been enough insight to be Amazon.
He doesn't have private equity origins as far as I know. He came from DE Shaw, a very well respected and long running hedge fund.
Evidence suggests that maybe they were. "Focusing" obviously didn't work.
But at the end of the day, it was private equity and the hubris of a CEO who wasn't nearly as clever as he'd like to have thought he was.