Actually, the way I read that description, they are difficult to damage using nerve blast or firestorm chips.
Also the description of the "exploding gas" seems to imply more dmg from burn weapons (I.E. Laser as opposed to Longsword)
I'm guessing that description was made during a time when
MA was planning to give each mob their own armor stats, just like our armor.
But according to almost everyone else,
Ma doesn't seem to have done this.