Ubiquity Edgerouters' management interface has a MongoDB backend and I have one on my desk at work, but I would not consider that I run "MongoDB" to provide services for my customers.
In much the same way I wouldn't say that my site is powered by Microsoft Excel; but you can be sure Microsoft Excel is used in my company.
I think they mean for first party backend tools. For example at my job I would say we use react in production - not on the frontend, but only for an internal warehouse application interface, nobody outside can use it but it's vital to our business, and we're the ones who built the application.
In much the same way I wouldn't say that my site is powered by Microsoft Excel; but you can be sure Microsoft Excel is used in my company.