I was wondering if he meant copy fields from one column to another, or to modify a value in a document based on the value in another field. I don't think that's possible in Mongo without writing server-side JS or doing it in your client.

Agree with your general point, though - this seems like they have a product/tech mismatch. Though I'd argue that this isn't a niche - read heavy, mid-scalability is a lot of the web.