I’m just going to mention this just in the possibility it helps someone.
I was having an issue when I was only halfway through the video where I rotated the “stem” of the lamp, and the “arm” of the lamp wasn’t following along with the rotation. I played around a bit after searching for help, and my solution was this:
I went to Object Mode, clicked the Armature -> Went into Edit Mode -> Clicked both of my bones and tried to parent with [Ctrl]+[P], at which point it said something like “Connect” as an option, and I clicked it.
For reasons I can’t explain, the model now rotated as expected. It seems possible my 2 bones somehow got disconnected or perhaps some sort of mystery occurred?
Don’t know if this will useful to anyone, but I hope it might be.