I think they mean "use the software" as in using the actual source code of the software in some derivative work or as part of some other application, or downloading and redistributing it for a different purpose, and things like that, not using the end-product application. They could stand to be a lot clearer about that, but their whole goal is just to prevent mega-corporations from being able to freeload off their work to make money off their software, not to prevent random people from using their software in certain contexts that might be construed as "commercial" in some sense. They mean not using the software for commercial purposes in the sense of not selling the software, not simply not using it for business emails or something stupid like that.