Okay, I just looked it up.
I kinda like the idea--especially since I didn't see Whedon's name anywhere near it--but I'm not a fan of prequels.
Sequel, old boy, sequel.
This is post-war.
Its a prequel to Agents Of S.H.I.E.L.D as its about the origin of that organisation. For Captain America, it is a spin off, not a sequel.