I think it's a matter of Fighting being, at least at the time, a "superhumanly strong" physical attacking type, with it contrasting the Normal-type as a "physical skill" type. Normal was the basic universal "physical attack" type at the time, with moves that were basic physical attacks like Body Slam, Take Down, Thrash, Slash, Double-Edge, etc. and Steel resisted that, while Fighting was the "unusually strong" physical attack type, the idea being that Fighting-types and their attacks are so strong that they can deal significant damage even to the most durable of physical material, with strength that far surpasses "Normal" physical strength (which is depicted in the Normal type, which is not very effective against Steel).
This shows in how the epitome Pokémon that embodies the Fighting-type's essence is none other than Machamp, whose gimmick is that it is inhumanly powerful with extremely strong muscles across its entire body, and it has so much physical strength that it can deliver extremely strong physical blows: a single punch from Machamp is so strong it can send the victim flying over the horizon, and it also has the ability to rapidfire deliver powerful punches and chops within seconds as a massive flurry: this combined makes it a physical force beyond normal (heh) physical strength. Its massive physical strength is so immense that it can effortlessly lift even a dump truck, and it can not only deliver a megaton strength punch to send an opponent flying, it can even effortlessly throw things across the horizon. Machamp is sort of the embodiment of the essence of the Fighting-type, and many Pokemon of that type are at least similar in build, such as Hariyama, Heracross, Conkeldurr (a direct expy of Machamp), Bewear, and so on and so forth.
But yeah I think that's what they're getting at: Fighting as the superhuman level physical type that has strength that can bypass most means of physical defense. It contrasts Normal in that regard, which is the basic physical type in the first three generations, and that type gets resisted by both Rock and Steel, and Fighting exists in relation to it as the superpowered version of physical skill type.