I think if you want to use the appropriate analogy, you have to include that it was fundamentally a public thing to do, even though she believed her audience tiny. Your analogy as presented gets confused because of the social conventions against eavesdropping, even in a public place. A tweet is fundamentally meant to be a broadcast to the world, not just your immediate followers.
Rather, imagine her shouting it out at a mall on a day when the mall is relatively empty. (So that she had reason to believe the audience tiny, but still broadcast it) Unfortunately for analogy-world Justine, a news crew was downstairs shooting B roll for background and she's there clearly visible and audible in the corner of the screen, and the clip got leaked. That's the analogous real-life situation.
Rather, imagine her shouting it out at a mall on a day when the mall is relatively empty. (So that she had reason to believe the audience tiny, but still broadcast it) Unfortunately for analogy-world Justine, a news crew was downstairs shooting B roll for background and she's there clearly visible and audible in the corner of the screen, and the clip got leaked. That's the analogous real-life situation.