Thellim isn't trying to read people's minds when they're not speaking, so she's not picking up any extras of their surface thoughts. Who'd just do that without explicit permission?
She's also slightly confused by the implication that Vanyel would take offense to true statements that are common knowledge - Vanyel hardly seemed that undignified - but she's probably missing some connotation or implication of what she said that is much less true-and-known. Maybe there was a translation failure, and it sounded like she was calling Vanyel a metal stick for beating people until they fall over.
:Vanyel tentatively suggested that the 'Eastern Empire' might do it, though he didn't know yet which books they'd be looking for. But surely Haven has some market research specialists specialized in international trade demands? We need not deduce all truths through only our own knowledge.: