The colour scheme is very "reichsgard knight" looking. Admittedly I know practically nothing about age of sigmar, are these guys the equivalent of the empire
from what I understand thus far the humans of the old world are scattered in lose tribes/communities for as far as they are still alive.
the stormcast eternals are basicly "worthy" humans who Sigmar has wisked away from the battlefield since his godhood started up to the endtime. to reforge them into the stormcasts. a bit of a mix of space marines and the fallen from valhalla in norse mythology.
TL;DR I don't honestly know. but personaly I don't think they are.