I don't think the world cup shouts are completely insane, however, maybe premature. Not sure the exact date the squad needs to be confirmed but I doubt he has enough games to put himself at the top of the Kane backup list.
If we are looking at two games and let's say he scores in both and/or generally impresses, then it wouldn't totally surprise me for Southgate to take him as he has been in a few squads and Southgate is a loyal person to players who have done well for him (although Calvert-Lewin is not one of the players like Pickford who has shone on a very consistent basis).