There’s no way that someone famous would bother making an account on Lemmy by themselves just for this unless they already understand what it is in the first place.

This is a very great point. Even if us lemmy/kbin people (with or without Victoria from Reddit) have taken care of all the logistical concerns on our end, there has to be some support for the guys on John Oliver’s end–even if only to guide them (probably the PA helping John) with the account creation process, giving a quick rundown of the UI elements needed to post replies, etc.

It basically requires a host to conduct it like a regular interview.

I thought this is what generally happens with celebrity AMAs.