- Sales people, account managers, etc. for their Teams product.
- Sales people, account managers, etc. for their Enterprise self-hosted product.
- Sales people, account managers, etc. for sponsored tags, collectives, etc.
- Support for the above (and the public Stack Exchange sites).
- Engineers for the above (and the public Stack Exchange sites).
- Community managers (who, among other things, fight abuse).
It all adds up. From what I remember most people working for SO weren't engineers, not even years ago (many were involved with the jobs site back then). There used to be a "Our Team" page which listed everyone who worked for SO, but it seems that's gone now.