The article literally says "Arcanine is actually a pretty decent Gyarados counter. If for some reason you are without a Jolteon, Ampharos, Magneton, Dragonite, Tyranitar, or Golem, Arcanine will rule the day against it." and explains that Arcanine's currently available fire-type movesets are strictly inferior to those of Flareon and Charizard.
Reading is THE TECH these days.