They probably use a solder pot at the "factory " ( otherwise known as some small area in a corner) to do the enamel removal and tinning, so the easiest is just to use a disposable lighter to quickly flame the wire ends, which, while removing the enamel, will also tell you it is CCA or actual "mystery copper" that they used.
there is also a lot that use tinsel wire, which is a copper strip that is wound around a polyamide core to make it flexible and strain resistant, and to solder to that you use the lighter thing or a solder pot.
If you do not want to use the BIC method, a soldering iron set to 400C, rosin flux solder and a big blob ob the tip, while simultaneously putting the wire and fresh solder into the blob to provide flux works well. Takes around 5 seconds of holding the wire there, and having something underneath to catch the drops of molten metal that fall down.