Planet Coaster - World's Fair Pack

I have a question: I currently see on Steamgifts giveaways regarding Planet Coaster - World's Fair Pack
These keys probably comes from Humble but it seems to me that it's not for the DLC only but for the game + the DLC. So if you already have the game, it doesn't work and Steam will put the message "Product already owned". That's right? We can't separate the game Planet Coaster and the DLC (from march 2020 humble bundle choice)? Where do these keys (Planet Coaster - World's Fair Pack) come from?
I ask this question because a friend has a Humble Planet Coaster key he would like to give and he would like clarification. He thinks that his key, which comes from the Humble choice of March, must be offered like the whole game and the DLC and not just the DLC.

I hope I am clear enough in my development :)
Thanks for your help!