In most cases, I think it is just a matter of lumping groups together, at least at the level where the press is national coverage and we would assume the reporters and newscasters are reasonably intelligent. Local coverage of news events elsewhere often get their cues and news feeds from the national organizations, so if it is summarized incorrectly there, anything that is incorrect is passed on and elaborated on, with a greater potential for the "reporter" to interject their own subjectivity.

I mean, it is a lot easier to lump groups together than to have to spend time explaining / learning about / understanding the whole difference between groups and the history of how they came to be. And, we as LDS church members tend to lump groups of non-members together as well. We don't tend to distinguish between the various distinct groups within judaism, catholicism, baptists, evangelicals, lutherans, or what have you.