Instead of asking why someone left after a month and felt compelled to tell future applicants what the place was like, the business chose a classic management solution: send a threatening email, demand silence within 24 hours, and hope fear performs the work. Instead of, say, decent leadership.
Companies like this one seem to believe they have discovered a brilliant loophole in reality. The review did not name names, except the company's of course, but it turns out it was detailed enough that the people could recognize themselves, which is awkward because that is generally how criticism works. If a person reads a description of their own workplace culture and immediately thinks, "This is definitely us," the issue is most likely NOT that an anonymous former employee wrote it.