Basically what he means is that since it is a "Profile Limited" game, SG can't detect whether or not people own the game. Since that is the case, people that DO own the game are able to enter. This usually happens by mistake, as they may not even be aware that they own the game.

The best thing to do is to check the winner's Steam Profile to see if they own the game. If they have a Private Profile or their games hidden, you can request them to allow you to check. I believe you can do a reroll if they refuse. I am not 100% sure about that, however.

Until SG finds a way to detect games of this sort (heck, DLCs that are Profile Limited can't be owned by anyone, and that includes people that own the base game, so don't make any giveaways for Profile Limited DLCs), there is no way to make it so only people that don't own it can enter.

Thank you for the giveaway. I checked, and I definitely don't own it. :)