A White House official said that Trump's preparation
This could easily be more of CNN's now famous anonymously sourced fake news. CNN has an interest in pushing Trump to 'testify', if you can call it that since there is no crime, before the Witch Trial board.
This 'report' as CNN calls it, could be CNN's way of keeping this idea in the news. So now when Trump does not interview, CNN can play it one of two ways or both. They can play the theme of, 'What is Trump afraid of!?' Or they can go with the, 'Trump flip-flops on Mueller testimony' theme.
Either way, it is another lead story for CNN for a at least a couple of weeks. And certainly without a doubt, the way the article is written CNN could have easily just made the whole thing up out of thin air.