What is culture?

One of our tutors at seminary made a remark to our Formation group about cell phones. He said that he, as a white person, would not answer his cell phone in a meeting, but he had observed that it seemed to be black African culture to take calls whenever wherever. He gave an example of a minister who took a call while preaching - which he did find unusually extreme, but it was an example of what he had observed.
Now, most of us would agree that this does describe black African behaviour regarding cell phones. But the black guys in our group said, 'no, that is not our culture'. This is similar to what I posted previously where black African people in one of my groups asserted that witchcraft and witch hunts were not part of African culture.
What do we mean by culture in South Africa today? Is behaviour practised by a definable group part of that group's culture? Does it need to be a traditional practice (I mean something practised by previous generations) to be culture? What I think is happening is that culture has become a concept used to legitimise behaviour. 'I do this because it is my culture and you may not disapprove because it is not your culture and you do not understand'. In fact the whole meaning of the word culture has been distorted. When someone says, 'this is not part of our culture' it really means 'I do not think this is legitimate behaviour, therefore I choose not to acknowledge it as part of my culture'. This is ok, up to a point, but it does entail a denial of the fact that certain practices, even if they are illegitimate, do form part of certain people's contemporary culture - or culture of origin. In the long run, pretending that a harmful practice does not exist is not likely to lead to a positive change in culture.