It doesn't matter what words she uses, the binder caught on her intent, on the meaning she was giving her words, which was altered by her tone. Aes Sedai can make a completely false statement if they believe they're telling the truth. It's similar with sarcasm: they are saying one thing, and mean something else. By using a clearly sarcastic tone, Cadsuane made those words mean something else, something which was "true".

She wasn't trying to hide her meaning. By the tone, these words meant something like "everyone in Bandar Eban knows that", which isn't a lie. Not a shred of an attempt to deceive in there. RJ made it very clear the first Oath doesn't hinder Aes Sedai from using sarcasm and exageration at all as long as they don't intend to hide the sarcasm in order to deceive (he gave the example of a blind person asking the colour of something. AS could not answer sarcastically for that, but if the person saw normally they could use sarcasm and say "it's obviously black" - their words meaning "what sort of question is this, you can see as well as I it's white".

In these cases, it's all about intent. They can mislead by omission too, because the oath stops them from speaking out lies, but doesn't force them to finish statements. They mean to say one thing and end up saying another by stopping in the middle.

Aes Sedai can speak hypothetically - in that case they are bound by the letter of the oath: presenting a true hypothesis without regard for the fact they hope it will be taken for a certainty (as Sarene did with Semirhage: it was a chance in a million that Elaida (or Egwene) would be convinced the woman knew too much to be executed, but that chance in a million was enough for Sarene to say "we may be able to convinced her to lessen your punishments" etc.). There the intent is to deceive, but the "may" makes the statement hypothetically true, so the binder doesn't stop that either.