It might seem like a mere conspiracy theory to some but current players are concerned about the depth of the corruption. ICC now investigating the media leaks.
One thing why I believe McCullum to be speaking the truth is that he is not even the slightest bit worried about repercussions, more that fact that his confidential testimony was leaked. Thus, because he did nothing wrong, he has nothing to be worried about.
Cricketers have a responsibility to report approaches when they occur so I don't think BMac is completely off the hook.