How did the Rams get this good at run blocking?

Agreed! Always an interesting one: can't (as in shouldn't) be understated or can't (as in impossible to) overstate :)

Is Martinelli playing better/playing differently this season, or is he just getting better luck? How much of perceived or actual improvement a function of him playing less?

It feels more Harry Kane at Bayern to me. Career marksman just piling up goals for an offensive juggernaut against lesser mortals.