What a strange statement. "We support their right to criticize their working conditions, only actually we don't at all"
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.