Stories like this are bizarre. There are a million ways to ensure rights for a founder-owner that do not depend on 51% ownership, such as requiring supermajority votes for replacing the CEO, or right of first refusals granted to the founder-owner for share transfers. If they throw a fit about those terms, then don't do the deal!
If you are selling shares to a PE firm with the explicit goal of retaining control, and you have less than 50% of shares, why would you make it so easy for them to get control?
If you are selling shares to a PE firm with the explicit goal of retaining control, and you have less than 50% of shares, why would you make it so easy for them to get control?