I would think that their old system of stack ranking would have had that selection impact. It has been gone for a long time but could it have had a lasting impact on company culture by who was being kept and who was promoted into positions that are responsible for the culture today? I don't think such a thought is unreasonable.
I only know a tiny bit about stack ranking, but I would think just the opposite... wasn't it designed to (at least partially) select for more conscientious employees?
