It's a reporter with a juicy story. Just like with Woodward & Bernstein with Watergate, someone smells a Pulitzer coming if they can single-handedly trigger the collapse of a beloved unicorn.
This reporting team already has a Pulitzer for their medicare fraud piece a few years ago.
That might be a little premature, but this team (primarily John Carreyrou and Christopher Weaver) are clearly not going to stop writing about Theranos any time soon. Additionally, they've pretty clearly provided an outlet for people who seem to be itching for this story to get some sunlight, so they're scooping the world on the blow-by-blow of Theranos' interactions with FDA, Walgreen's, Safeway, etc.