Is this gray clip hook an original LEGO part?
This looks to be Arm Piece with Towball and Clip. 

There are quite a lot of copycats these days. So there is always a chance it is clone piece. To confirm this is genuine LEGO piece best thing would be to look for LEGO logo, but it is not always available on small pieces. Alternatively you can look for "30082" which is a part number.