I dug through the relevant support pages and found some information for you.
Short version: Don't accept things you weren't expecting from people you don't know.
Long version:
The Steam Support page on trading and gifts says...
[...] a gift sent to your account has been revoked. The most common reasons this will occur are:
- There has been a purchase error with the game you were gifted
- The purchaser has filed a dispute over the purchase
- The gift purchase was made using a fraudulent payment method
If you believe there has been an error, please contact the person who sent this gift.
The subscription to the gifted game is no longer valid. If you wish to continue playing the game without losing any game progress, you will need to purchase the game through Steam.
Warning: Never accept a gift from someone you do not know.
Meanwhile, a few pages away...
Redeeming Fraudulent Gifts
Never accept a gift from an unknown user. Any accounts tied to a redeemed gift from a
fraudulent source may be suspended.
In summary: You can either lose the game you were gifted, or possibly your account, depending on the whim of the Steam Gods handling your case. Expect the worst, because they tell you clearly in both areas don't accept things you weren't expecting from people you don't know.
Ask the person trying to gift or trade you the game to identify themselves, and reject the gift if anything seems suspicious. Better to lose a "free" game than your account, ne? If it turns out to be a friend or just someone who feels like gifting you stuff, ask them to send it through their real account, instead.
I tried sending myself a gift just now - the email contains the sender's email address, indeed. What you can do is send a gift to your own secondary email address, and send them the URL for redeeming the gift (the URL you receive by emailing the gift to yourself) . Hopefully you have some way of contacting them other than their steam profile; for example, give them the url written on a slip of paper.
Caution: The URL contains the email you sent the gift to. If you don't want the receiver to be able to guess who you are, and the secondary email you're sending to is obviously related to you, create a new email account to send to. Example URL, email highlighted:
https://store.steampowered.com/account/ackgift/1F631467BB7E?redeemer=Fadeway%40yahoo.com
With this method, the first time they learn the sender's name will be when they enter the URL into a browser:
If there's no way to transmit the URL to them without posting on their steam profile, that's a lost cause, unless you get a third person to act as an arbiter/organizer who friends everybody and distributes the links while keeping it a secret who sent which one.
Best Answer
I think it should be possible if your friend asks for a refund, and then you ask for one as well. It's explained in this article on Steam support: https://support.steampowered.com/kb_article.php?ref=6643-QEUV-0459
Once the refund is done, you can request your own refund and then repurchase the game to gift to someone else.
Note: it is possible that this doesn't work with this particular game bundle because you probably played together and thus together have more than 2 hours playtime. Still, I'd recommend putting in the refund request.