A midair explosion would show up as several planes on radar and have more debris fields over a larger area, some miles apart.
Though the size of the debris field might indicate a mid-air explosion, I wonder if a similar effect would be observed if the plane flew straight into the hard rock face of a mountain at a high rate of speed. Compare with the crash of United 93 on 9/11 - that crash was into soft earth at speed with few large pieces but the debris field was relatively small.