Uh, let's see, he correctly points out that auto attacks scale off a fifth power function (at least with respect to attack damage, as the damage from AS, crit chance, armor pen, and crit damage/IE's true damage on crit all scale with attack damage, so if you include the interaction terms, you end up with a formula that contains an 'AD^5' term as the highest power term. This makes the damage formula a fifth power, or 'quintic' function)
He then notes that this is different from orders of magnitude, but is in fact a difference in the powers of the respective damage and resistance formulas. The formula for resistance to true damage is literally just 1.0(HP), or a 1st power function of X where X is their total hp. This is also known more simply as a linear function.
He also contrasts this linear function for resistances to true damage to the resistance formula for physical/magic damage wherein you only take 100/(100+armor)[incoming physical damage] or conversely where your pEHP can be depicted as hp(1 + armor/100). Since this is effectively 1.0 hp + 1% hp per 1 point of armor, its a quadratic formula with respect to hp.
Are there any other words or parts of his comment that don't make sense? I assure you not a single word was used incorrectly, and the strawman at the end of your comment has nothing to do with the comment you replied to.