Cultural geography is, of course, about culture, but it is specifically about how culture is distributed across space.
For example, cultural geography can be concerned with the issue of how various aspects of culture have diffused across space. An example of this might be the study of how European influences have diffused from cities into the countryside in a place like Belize that was colonized.
Cultural geography is also concerned with things like the distribution of ethnic groups and ethnic identity. Cultural geographers of a place like Belize might look at the distribution of the various ethnic groups in the country. They might also want to look at how the presence of people like Indians, Chinese and Mennonites has impacted the culture of the regions where these various groups live.
In short, cultural geography does study culture, but it has a geographical component. It is most interested in the way that various cultural traits are distributed over the space of the country.