That was a piece of tempered glass, as we can tell due to the way it broke into tiny pieces. Due to the tempering process, where it's heated then quenched by l

That was a piece of tempered glass, as we can tell due to the way it broke into tiny pieces. Due to the tempering process, where it's heated then quenched by large fans, the glass is under stress that's concentrated at the edges, and especially the corners. This is why it explodes when they break the edge the way they did. Ordinary annealed glass would've broken into large, sharp shards, whereas laminated glass would form a break pattern like annealed, but would stay in one piece due to being attached to the plastic inner layer.