The mechanism would work this way: sales people exhibit multiple features, and they are promoted based on some combination of those. If a sales person has outstanding other credentials, they might be promoted despite poor sales percentile. Those other credentials might actually be better predictors of managerial experience. Conversely, many of the top sales people might have been promoted on the grounds that they were good sales people, without exhibiting any other skills.
Note that there might still be a positive correlations between sales skills and managerial skills, but due to how the promotions are selected, you end up observing a negative correlation in the promoted group.
The mechanism would work this way: sales people exhibit multiple features, and they are promoted based on some combination of those. If a sales person has outstanding other credentials, they might be promoted despite poor sales percentile. Those other credentials might actually be better predictors of managerial experience. Conversely, many of the top sales people might have been promoted on the grounds that they were good sales people, without exhibiting any other skills.
Note that there might still be a positive correlations between sales skills and managerial skills, but due to how the promotions are selected, you end up observing a negative correlation in the promoted group.
https://en.wikipedia.org/wiki/Berkson%27s_paradox