If I'm wrong I hope someone else can correct me, but I think that what they mean is that Microsoft fonts in general (that is, if nothing else is stated specifically for the font) are free to use for commercial use, as long as the commercial use (like a product) is produced using means that you have commercial license for.
Example: If you want to make a video game using Microsoft fonts and sell it, then you need to have a commercial license for the program you are developing the game with. Visual Studio, for example, can be used commercially without a paid license by individuals, but not by larger organizations.