She is self-employed and like many writers, writes as a free-lance which means the DM (or whoever) has no legal responsibility for what KH tweets as a private individual , unlike her articles for the newspaper for which the DM has legal responsibility, and a commensurately large legal department, one assumes. So what is there to misunderstand? Everybody else seems to grasp the distinction which is a simple enough one.
If she made a genuine mistake (as is possible) her intransigence and refusal to apologise right at the outset is what has led to this case.
Arrogance, pride, with an admixture of "any publicity is good publicity" , I think she got off lightly.