If they do actually know what the issue is, they certainly haven't actually told anyone. They've only given generic and sort of hand-wavy "we fixed it don't worry" kind of explanations.
You're right, their statement now it's pretty clear. Initially, things were worse. They give out conflicting information to different people, no one was really sure if it was a recall or how to handle it. That was weeks ago.
If I had to bet it'd be that they don't know what the issue is, given the PR damage of combusting replacements.