One guitar per side is double tracking, and its whats clearly audible in the full mix, and pretty normal in production of metal.
Edit: two per side is called quad-tracking. Also pretty normal in metal. Its usually one or the other. Layering formats that get less look-in are ones with one or more centre tracks.
So yes, whoever wrote that wiki is at least using some odd terminology, very different to what you normally find when discussing guitar tracking. At least they actually describe what they mean by double tracking, so that we can see that its not whats normally meant by double tracking, and that after saying it wasnt double tracked (their defintion: 2 gutiars per side), say that it was double tracked (normal defintion: 2 guitars, total).