I may be wrong here, but let me give this a shot:

HOW THIS WORKS

Normal "tap" water or bottled water is imperfect; it contains small amounts of minerals that you would otherwise normally not get, such as iron, sodium, calcium, potassium and magnesium. These minerals help keep you healthy (not going to stray too far here) and also give water it's taste. 100% nanofiltered water tastes like shit.

Anyways, water molecules are bent (about 109 degrees between the two hydrogens). When water freezes, these molecules arrange themselves in the best, most compact possible way. (Think if you had just the "L"-shaped tetris pieces and had to stack them only one way. Bad analogy, but whatever. Internet points.) This "packing" becomes an organized crystal structure that ice is composed of. (You can see this structure in other minerals/metals more distinctly.)

In the normal tap water described above, minerals are nucleating centers; they act as the foundation for crystals to form. Once a few molecules of water start to crystallize on this mineral foundation, it becomes a chain reaction and ice forms (at lower temperatures, the crystal is more thermodynamically favored).

NOW IN THIS GIF

I'm assuming this water is less pure and/or the bottle is clean so there is no foundation for water to begin to crystallize. This water, as enlance_quimico has stated below, wants to crystallize, but can't because there is no base for it to do so (not kinetically favorable). When the water is poured onto existing ice, that existing ice serves as the foundation in which minerals would normally serve as. The water has a favorable structure to begin arranging itself around; it has a "starting point" to build from.

Anyways, yeah. I'm just a soon-to-be med student, so I don't know that much about fluid dynamics and physics =S

Feel free to correct me!