He is using a soldering GUN, which is only appropriate for large wires and large objects. In general, though, the same principles apply. He gets it WAY too hot. See the big cloud of flux/lead vapor? Not good.
The first and foremost goal is to transfer heat from the tip to the wire. "From below" isn't much better than using a candle or match to heat the wire. "From above" is lame also because he is not using any pressure between the iron and the wire. Instead, he drips solder onto the wire from the hot iron, and creates a bridge of solder to transfer the heat to it.
Best practice would be to use pressure between the iron and wire, apply solder between the iron and wire, and let it flow, not "paint" it onto the wire. Always use rosin core solder, or either liquid or paste rosin.
Same technique is used with an iron and even with SMD devices, except that you tin the iron and control the heat better. Don't let it get so hot that it evaporates the flux (that big cloud when the solder touches the iron) and "cooks" the solder (solder gets rough-looking and creates peaks and strings), and most importantly, burn up your PCB and device!
Solder should NEVER be "painted" on. It should FLOW onto the joint.
Lead-free solder is special and takes special techniques and even special flux.