Help... Won a game... wrong game?

Try to talk with the person who made the GA, maybe he/she sent you the wrong key, or maybe he/she make a wrong GA

Contact the giveaway creator and explain that they have to give the game they made the giveaway for. If they do not "sort out a working proper key" then wait seven days and mark as received. At that point I would also make a support ticket explaining the situation and that it was obviously a fake giveaway.

Edit: Added the part between the quotes. Commenting before the morning cuppa is not healthy. FACT.

Looks like you received a game that was given free before, which is why it can't be made as a GA here.
You could wait until a week and mark it as not received, since you didn't get the game the GA was created for. You couldn't mark it as received, since that game wouldn't be added to your Steam account library. That would look like you violated the rules and didn't activate a win.

Looks like a typical case of "couldn't find the game in the list, chose a game with a somewhat similar name instead". In good faith, you should tell the creator about it in a comment on his giveaway, and wait seven days for him to take action. If he doesn't, take it to support.

I've sent a msg to them on their steam profile. I'm worried it was due to a translation error since they're taiwanese. I guess they're likely to cancel the GA or whatever but maybe i'll be lucky and they'll give another key. Thank you everyone for quick response.