It leaked to other people in the company, who were looking to use that information for a secondary market product that Carta had. Since they know everyone who owns stock in company X, they know exactly who to approach about selling stock in company X on their brand-new privately held company marketplace (without the companies permission). https://techcrunch.com/2024/01/07/carta-the-cap-table-manage... for more. After this was discovered and widely reported they sold their private secondary market to another company, because it was impossible to regain trust.

They are also involved in trading lawsuits with former exec turned whistleblower for two different people. https://medium.com/@jerrytalton/when-your-company-tries-to-c... is the former CTO's take on the situation. https://levyvinick.com/wp-content/uploads/2020/07/COMP-for-D... is the former VP of marketing's filed lawsuit, I can't find a blog post from her.

It's actually mentioned in the article OP posted, but if you want to read more you can here: https://techcrunch.com/2024/01/07/carta-the-cap-table-manage...