Larian's writing team are currently using the tadpole as an easy-out excuse for lazy or inconsistent writing.
If characters know things they shouldn't, then it's because the Tadpole links all of your thoughts, so they know by extension. Only it clearly doesn't apply to everything, when it's convenient for them to not know something.
When Gale confides a secret to you, because he trusts you, and not anyone else - it's a secret that he's revealing, and he's been keeping it from everyone easily enough.. but when he confides in us, then, suddenly, everyone knows, and can comment on it in party banter later - why? Tadpole, apparently - but why do they know when we do, yet not when it was just something that Gale kept to himself?
Further more, it doesn't apply to you at all - because they are all perfectly capable of keeping secrets from you whenever they please, about any range of thing, as long as it's the convenient intention of the writing that they keep it.
It's convenient for written dialogue when we don't know what someone else has been up to: So, for example, Astarion can inform us that he hunted a bear - we don't know in advance, just so that the dialogue can happen, just as we don't know about any of his other activities while we're not around, before the big reveal. We don't even know about his vampiric thoughts regarding his appetites and his companions, before the reveal - he keeps all trace of that hidden from us, apparently, because the vampire reveal needs to be a 'surprise'. Similarly, Astarion doesn't know that we encountered a hunter, if he wasn't with you, until you have a conversation with him and tell him about it - why doesn't he know? Because it's written lazy and inconsistent.
