@seekermoc
Well, he does say you need 3 special numbers to specify the metal; relative weight, melting point and atomic weight.
Really don't know how you'd get those without modern technology. And even then, it's scale-dependent (e.g. most countries in our world use Celsius, but maybe, the fantasy world uses something different, maybe even Farenheit!!!!).
I think the author was trying to get at, it's hard to spot the pattern without isekai knowledge (and to begin with who tf remembers atomic weights and crap anyway).