Your "mystery glue" most likely is NOT "hot glue". The mass production builders use Jigs and microwave cure glue. Glue that cures when exposed to RF energy. http://www.p2pays.org/ref/10/09081.pdf is one example of the general technology. I couldn't find a specific example on short notice. The parts are laid in the jig all together along with the glue which remains un-cured and flexible until radiated. Then it is radiated and cures. Completed parts/subassemblies are moved to the next jigs and more parts applied before radiating again. Cure times are very fast using this material.