So public is only when there is a mic or journalist around? Dubious.
No, nothing to do with electronics, more to do with intended audience. The journalist part might make it public, or potentially anyway, depends on the context. You've heard of people talking to journalists "off the record", right? Well that supposed to be a gentleman's agreement that they are no longer speaking publicly. Probably foolish to trust the journalist, but that's besides the point.
Whatever the blurring of the boundaries may be, there is a clear distinction between public and private speech.