yes, the bottles are "melted" but it is done in a glass kiln, at a temp of 1200 to 1400 degrees and kept at that temp for anywhere from 1 to 3 hours and then "cooled" from 3-6 hours.
Kiln work can be tricky at first, it would be best to first know how to operate a kiln and know what type of glass to be using. A great website to check out on fused glass(melted glass) is warmglass.com. Good luck.