Call of Duty: Black Ops Steam Altergift ?

Let me guess: the seller was wildboy? :D
Either by mistake, script error (when creating new offers or adjusting prices) or - if it happens several times - scam attempt.
If an offer looks to good to be true, it usually isn't an offer.

Maybe someone sold it at that price and GG didn't update prices in the meant time.

On another site (those we can't mention) a copy goes for 0.87 cents but when you go further it goes for 40 euro.

I am guessing keys were cheaper then gifts.

There is a 3 letter shop that sells it for 11 euro, dunno how legit it is, it's also EU restricted.
Nah, never mind thats a russian version even though they sell it as European, weird.

Those sites (ITAD, GGDeals) don't update in realtime. Prices are off sometimes.

as others said... if it is too good to be true than it is... most often it is a pricing error and usually corrected pretty quickly but these deals sites might not reflect the actual price due to some delay or sync issue.

Basically the sites list it for that price to get some people to visit their shitty websites and when you buy it they cancel the order anyways or you can't buy because price already changed. It's just a scam by the site owners.