I honestly wouldn't interpret too much into that artwork. The foot is in a similar pose but not 100%, all the Possessed have wings and can actually fly which hasn't been so far in the game either, there are Sanguinary Guard or whatever flapping with real wings and there's a Gravis Captain with awesome custom armour without such a model existing either. Also all the Marines etc. there are clearly painted and not taken from some 3D file which is probably the biggest argument against it.
It's a great piece of artwork no question, but it's just that.