For comparison, this is what gamesieve lists as free games. I see a couple at the top (most recent releases) that are still missing from your permanently free games. edit: but I also see that they've all been reported in this thread already...

I would say it's more of a mistake since GWYF has never been on GOG and there is no announcement that they added any other platform besides Steam and consoles.

Given Luna's existence, It's odd to me to include a Steam game when they don't include that platform on it, unlike GFN.

Or maybe the game will be also released on GOG?

Per my last post, they didn't even make any announcement. If someone is starting a rumor, it would have to be base don the blog from Amazon.