That wasn't merely a "security vulnerability". It was also a demonstration that the people running the business have absolutely no idea what they are doing when it comes to security, privacy, or testing and release processes. (Actually, there is an alternative explanation, which is even worse: they knew and didn't care. I prefer to assume naivety rather than malice.)
Unfortunately, the only sensible action when faced with a business like this is to run away and not look back for a very long time, except perhaps to check who the people responsible were so you can avoid anything else they work on in the near future as well.