Say you know someone, but you lost contact with them for a while. For a decade. For a year, or a month, or a day - or even an hour. In the meantime, they keep changing from their experiences and whatnot. What do we call someone who you used to know, but they changed so much they might not be like you remember them, not at all? An old friend.
What do we call someone whom we don’t recognise? A stranger.
Strangers up to now, have just existed at people. As of e87, Night Vale citizens are turning into strangers. But that is not all - consieder the circumstances. Who was in the courtroom? Judge (who didn’t listen to the Whole Truth), the lawyers (who, given their reactions probably covered their ears), stenographer (who already knew he would be incinerated), the jury (whose reaction to the Truth is ignored), bailiff (same) and people (who didn’t ollie out in fear of some unknown - to them - fallout). And the latter three were ‘replaced‘ by strangers. Maybe they changed because of the implications of the Whole Truth?
Ship of theseus means that everyone in nv is a stranger to be.
And who else is implied to know about the Truth? Our radio host.