When USCIS says that your case is being held for review, it means that your interview was scheduled but the officer decided to hold your case to review your case. They have to give a reason for doing this. In some cases, the hold is caused by missing or inaccurate information on your application. In other cases, the hold is due to a violation of the immigration laws.
Reviews are based on information submitted by the State under review, including national reports; information provided by independent human rights experts and groups (known as “Special Procedures” or “troikas”), and human rights treaty bodies; and voluntary pledges and commitments made by the State under review. Time is also allocated for questions and comments by member and observer States as well as NHRIs and NGOs.