So would you like a fine for your bugs? And note that contrary to other professions, software development doesn’t have generally agreed recipes for building bug-free software, so was that really negligence? Was it malpractice?
Being fined for a contribution to an OSS project would be terrible, wouldn’t it? And no, the size of the company doesn’t and shouldn’t matter in the eyes of the law, only the impact.
Also people uploading stuff on the Internet should really expect a best effort privacy. If you expect secrecy, then uploading shit on a platform meant for sharing is pretty dumb.
Note that I will blame Facebook for willful privacy violations. And I hope to see them suffer under GDPR. But a bug doesn’t fall in the same category.