The basic idea is that in fluids, adjacent particles can swap places instantaneously, so the fluid can flow. In solids, adjacent particles can't swap places, so they can't flow.
However, that's actually just an ideal. All fluids take a finite amount of time for the particles to swap places, and many solids can have the particles swapping places, just they take a long time for it to happen.
So "solid" lead or glass will flow, if you give it long enough, and if you do stuff quickly enough to water, the particles won't have a chance to flow and it will behave more like a solid.
Another way of seeing the effects is to do what they do here - use a thick suspension of cornflour in water. Because the particles are big, they are very slow to swap places compared to most fluids, but still quicker than solids. So if you do stuff to the suspension very quickly, the particles won't have time to swap places and it'll behave like a solid. But if you do stuff to it very slowly, the particles will have time to swap places and it'll behave like a liquid. The results are as seen in the video...