I think the Warmastered edition is added automatically to your library if you own the normal version, so this key would add both versions, normal and warmastered.

For future refference, as written under https://www.steamgifts.com/about/guidelines : "Giveaways should accurately reflect the game being given away. If the game is not available in the giveaway list, please contact support to have the game added, instead of posting the giveaway under an incorrect name."