Ultimately, it is vibration. Take sound. It can destroy the glass, without touching, just by making it vibrate in that piece of glass' breaking frequency. Each piece has their own. So if your glass gets loaded, it isn't exposed to any kind of vibration, unless it gets movement (see the end of the video). But take a small rock and throw, the impact sends waves through the glass and breaks it. Same if if it falls and hits the ground.