After some learning and research, I can somehow understand it now. Basically his way of reducing the normal intensity is a ‘old’ method i think, today we can use flatten normal instead. And he creates the specular with just reducing the value.
As for the normal maps, yeah he is animating them in a very slow speed which looks as if it is not moving.
Updated: But I having new weird problem. I make a new material and copy all the nodes from the original material to my newly created material. When I insert a instance of the new material into my scene and edit the color parameter, it is looking black. The nodes are the same but somehow the result is different.
Updated #2: My decal material turns black when zoom in, I thought it to be a material problem but turns out to be a very simple problem relating to the X scale of the decal. It is in the negative range which causes the blackness. Just need to scale it to positive and it’s fixed.