Without seeing the actual policy, my guess is that "criticizing" is something employees can do internally within the company. However, you can't post public tweets about it.
In other words, "don't air dirty laundry".
This type of distinction is very common in typical employee policies. Likewise, it's common for a CEO for VP to say to the employees "I have an open door policy so if you see something wrong, tell me." -- but common sense should tell you that the CEO does not mean for the employee to post an "open letter to the CEO" on Twitter or NYTimes for the public read as well.
I know of no well-known company that encourages employees to publicly criticize their workplace.
Either way, Im sorry to hear that things went south after complaining and it sounds like it just got bruised egos involved.
And they will come down on those people HARD! "Why is your employee complaining to me? Why aren't you doing your job?"
And down the line it comes crashing down. And meteor lands on your face.
Reminds me of this news.yc thread, "We may get fired and I don't know what to do" [0], which had a follow-up from the OP with full backstory ~7 years later, "I stood up to my boss, then he got promoted" [1].
Did the same a while ago, with my CEO. Instantly removed from overseeing the biggest project we have in the works. Also removed from all communications about the project and privileges to view project-related documents revoked.
https://news.ycombinator.com/item?id=20227175
https://www.washingtonpost.com/news/morning-mix/wp/2018/02/2...
Or worse, threatening to make his choices look incompetent.