Re: Actually (effectively) incredibly secure then...
TB correctly noted, "...sizeable 'unless' [someone shared link]..."
But it's also multiplied by the small fractional odds of anyone noticing the shared link, those noticing actually viewing, noticing the live private data, capturing said private data, and then misusing the data. It's not surprising that nothing came of it.
Still, the initial observation is ultimately correct. Just not any significant risk, unless repeated endlessly. So corrective action to prevent recurrence is A Very Good Thing.