My guess is you're right. Many companies have terms in their employee agreements limiting what employees can say/post about the company publicly, including via social media, YouTube, and so on. Many are extremely restrictive and enforced regularly. For example, good luck finding a non-throwaway HN poster self-identifying as an Apple employee. I don't talk about my employer here or even contribute to threads about it. These agreements are very common, check your employment agreement--you might have agreed to one, too.