This is because it hasn't launched yet. I think pre-order games don't show up on the list for other people. That's also why they can still enter the giveaway.

I also own it and still can enter.
It's not present in Games list on SG account page. Also I can't see it in my Steam profile games list neither on desktop nor in Android app.
But game is not marked as private in my library. I guess it's some kind of pre-order thing.

Upd: just checked games list of my Steam friend who bought the game today - it's also not listed there, but on store page I can see that he owns it as well as I can see entry on Activity page.