Normally that would mean that he set his meter to ISO 400 and asked the lab to push two stops (from normal), even though ISO 400 should require a three stop push from ISO 50. A three stop push, though, might have been unacceptably contrasty, and maybe his meter was overexposing a bit, so it's possible that based on his tests, a two stop push looked better to him than a three stop push. "+2" is just what you tell the lab when you want a 2-stop push.

You can't tell much about the grain from a scan of that size.