Relevant tweet further down: https://nitter.net/karrisaarinen/status/1743407369512743094

> Buy price was exactly our series b share price. The angel investor in this case was a family member whose investment was never published and hardly online. Yet he was contacted directly to the email he used with Carta

As said before, it is not impossible that the buy price was determined using public information. However, he is definitely implying it would be impossible to know the identity of this investor if it wasn't for Carta sharing private information with Carta Liquidity.