Generally in slander/libel I think the defendant needs to prove what they said/wrote (if not fair comment) is true. The claimant doesn't need to prove that the defendant knew it wasn't true.
Yes - I see. I suppose the problem comes if the defendant thought it was true. That is, Bong says 'pretty sure I heard him say...' And unless there is incontrovertible evidence that JR didn't say what Bong thought he heard him say, it will be really tricky. It all depends on what Bong said in his interview in French with at least two different translations that I've seen.
Murky waters ahead if there is any court case.