What price privacy?

God knows I hold no brief for Donald Trump, but clearly what was said on that bus all those years ago was meant to be a private conversation.  So the question arises - (1) who recorded it and why? And (2) who put that recording into the public domain, and why?  Perhaps the second question is more easily answered, but the first is more crucial.  Was this yet another case of somebody being caught out by an open microphone, or was this a case of a private conversation being deliberately secretly recorded?  As I've said before, does this mean I need to sweep my house for hidden bugs before having friends round for a chat?