Basically, the way the conversation went was as follows:
The Chosen's player asked if his character had a title in-game (like the Slayer), and I said, "Well, what do you think?"
Another player (playing the Flake) then responded that I should 'stop doing that', i.e. offering the player the opportunity to answer their own question.
I then explained that there was no fixed setting as such, that my job as Keeper was to ask them leading questions about their characters and the environment to build up a picture of the setting.
The Flake's player immediately responded with: 'that's stupid though[...]With an IRC game you need to have some planning to it'.
That was pretty much the extent of his argument and I was feeling too frustrated at the time to try and argue the point. But I spoke with another player, and she said she'd been thinking that maybe for IRC there needs to be a seperate world-building session.