oh man that guy is just doing a horrendous job of it. if you want to do it right, first, make sure the wires are nice and clean then twist the wires together, second, heat the twisted junction real good with your soldering iron, THEN, third, apply the solder to the heated wire junction. you know the wires are at the right temperature when the solder runs all up in the strands and stuff. it should just wick right into the wire, if you're working with stranded. for bonus points, apply some solder flux paste before soldering; HOWEVER; most common electronic solder comes with a core of rosin flux, so, it is more or less "self-fluxing". once the solder dries, fold back the soldered junction, (edit: then, spray finished work with a blast of flux remover or contact cleaner to get rid of flux residue and soldering by-products) then slide back the heat shrink and shrink it up to finish the job. what this guy demonstrates is absolutely what you DO NOT want to do: insufficient heating of the wire; the solder is just beading on the surface (way too much was applied, as well) and not penetrating the joint. the job the guy in the video is doing, the wires are pretty much only being held together by the heat shrink. i bet you could pull that joint apart bare-handed without too much exertion.
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