Well if what I saw was accurate, Ash-Greninja and Altaria are the first Pokemon in that match up, or if not, then Ash-Greninja is the ONLY Pokemon IN that battle.
And I can't imagine they'd only show us the final battle given that Ash is LATE to the battle.
Yeah for example, Marcargo's temperature reaches 18,000 degrees, and before anyone argues it's only a Pokedex thing, no I'm pretty sure it does reach that temperature in OUR universe.
While I'm sure in the Pokemon universe, it exerts the equivalent of whatever a human would be safe around. And even if that's not the case, it shows humans in the Pokemon universe can survive that high of a temperature, compare that to other elements. The metals in the Pokemon universe have to be stronger than our universe.
Take the sharpest object in our universe, and I highly doubt it'll even scratch a human from the Pokemon universe.