It's the usual vapid mainstream bullshit, tied in with the usual vapid prog nerd inability to comprehend basic music theory. This dork probably wanks it to Opeth. Nonetheless, it's part of the emerging consciousness of metal as more than stupid, burnout noise. There are obviously opportunities for promoting real music out there, but glomming on to the dubious credibility of jazz isn't the best way.
The most obvious bullshit here is the assertion that metal is primarily an 'improvisational' genre (though this was merely the most egregious error among many). There was always a tension in rock music between the directionless, improvisational spirit inherited from jazz and the unidimensional focus-grouped polish of commercial pop music. In breaking with previous generations of rock, metal, ambient music, industrial, some hardcore and, to a certain extent, the early generation of 'alternative' rock all made end runs around this dichotomy by making music that was at the same time complex and multidimensional, but also deliberately composed for effect, rather than just being jammed out in the studio. Instead of heaping praise on dumbass postmodern hippies like Steve Vai and Zakk Wylde, the article should have focused on artists like Atheist, Deicide, Morbid Angel or Seance, who borrowed tonal and harmonic elements from jazz to enrich their expressive lexicon without getting caught up in the more defective elements of jazz (i.e. the emphasis on improvisation over rigorous composition). But, of course, this was written by a douchebag who thinks video games lead to musicianship, so we don't get anything so useful.