every DLC on steam will continue to show up as a giveaway on SG unless you click the eye icon next to it, regardless of whether you own it or not.
If you won it from SG before you won't be able to enter, but you'll see the giveaway.
Unless you use some third party thing to remove those giveaways or turn them off yourself one by one, they will all appear on your possible giveaways. That is not an issue from SG, this is entirely due to how Steam interacts with 3rd party websites like SG