Probably the most important to emphasis:

-He is in the process of creating a 3D printer, more specifically a 3D printer extruder, that is capable of printing using metal filament.

-He based his idea on that of traditional FDM 3D printers – the ones that print in plastics, by melting and extruding molten PLA or ABS. He simply replaced the plastic with a metal alloy (solder), which consists mainly of tin (95.8% tin, 4% copper, and 0.2% silver).

I can tell you he will have hard time with the oxidize layer that wont bond at all. Any people with basic soldering in electronics knows it is a pain in the butt to deal with oxide layers that prevent the solder forming a bond. But then even if he succeed making a bond, I will call hardly "3D printing".