[rmc]

They asked what my desired and walk-away salary was "to make sure my desired salary wouldn't sound stupid/outrageous to the company", also under promise of confidence.

A good way to even it out would be to reply with "Well I dunno, why don't you tell me what the company's desired salary is, and I'll tell you if it's outrageous?". After all, if the only reason they want to know is to prevent you sounding stupid, they'd tell you that, right? :P