Even the author questions what is being depicted, I agree it's too flimsy. Isn't it MUCH more likely that it is layers of non-metal material? Leather or cloth Lamellar. Or some kind of quilted linen cuirass for a horse.
Certainly if it is mean to be chain mail it is an odd stylistic rendering (which is possible) but given the realistic nature of the drawings why would an artist choose to depict only 1 thing stylistically as opposed to realistically? ( if you are not following me: it does NOT look like chain mail which is made of interconnected rings, not zig zag lines). Chain mail does not seem to be the most likely conclusion.
Still, you mentioned "'cataphract' style Iberian heavy cavalry." Even if it is choosen to be depicted as chain mail by the devs in a kind of horse unit available to Iberians... a horse with a chainmail hauberk is hardly a cataphract. And it would be a travesty if a chain mail blanket were treated with the same armor rating as a horse covered in armor plates...