It is really not that surprising. People talk. When you work for a company like this you end up with a large portion of your circle of friends being current or former co-workers. I knew things there were not NDA-cleared for years after I left various startups because people chat and if you know the right questions to ask or are reasonably good at appearing to know just a bit more than you happen to know then people will often fill in the blanks for you. The well really only runs dry when most of that cohort have also left the company.