Bright nickel plated terminals don't take solder well unless you scuff the surface with a fine abrasive and use plenty of flux. IMHO the demonstrator should have mentioned that if they are not gold flashed or tin plated, you'll probably need to pre-tin the terminals, then demonstrated that.
However its almost certainly not the demonstrator's fault - any chief engineer of a radio station is almost certainly competent with an iron in their hand - its the fault of the magazine commissioning too short a video and scripting too much in it. 4:06 or 246 seconds isn't a lot of time when you take off 20 seconds for opening and closing titles and another 15 seconds for a Menards 'Tool-Shop' brand product placement.