I feel that, if BG were indeed wearing a mask or a prosthetic nose (as one blogger speculated), etc. that this would've been made clear by LE or the family (the family who's been very open answering questions on SM). There would be no reason to keep that information secret, especially since they released the video still. In fact, releasing such information would most likely be helpful because, chances are, someone who knows him might have stepped forward and been like, "You know what, my brother left the house that day with one!"
To me, it seems clear that the reason they said to look at the rest of the body is because people are more than simply one feature. We recognize people in our lives not just by their faces but the shapes of their bodies, their clothing, how they wear their clothing, their stance, etc. That's how you can recognize a loved one in a crowded room, even when they have their back turned. There is nothing in that grainy video still that sets his face apart from the thousands of other men in the area. Indeed, we can barely see the face. By looking at the image as a whole, and not just as one thing, it might help people in his life identify him more easily.
