It's not required – to my knowledge – that specific person disclosing the information be in breach of a fiduciary duty, as one could easily overcome that by disclosing to someone who discloses it to someone else, who then trades on it.
The scenario you mentioned is generally understood to be permissible, but it's not exactly clear to me why. Perhaps that the information became "public" (whether intentional or not) when discussing it in a public forum such as a coffee shop?
The scenario you mentioned is generally understood to be permissible, but it's not exactly clear to me why. Perhaps that the information became "public" (whether intentional or not) when discussing it in a public forum such as a coffee shop?