Steam Gift link through email.

Well, you can always try to click with the correct and initially intended account :D Tell us how it goes.

Perhaps he did get it as a gift. Did you check his Steam inventory?

If it's a Humble Bundle link, it's still good. You have to claim it on that page to use it. Moreover, claiming would result in a Steam key, which would also be unused until activated on Steam.

You'd have to contact the seller and explain that the item was not purchased for personal use and would be sent to someone else, if it is a Steam gift window. If it is a HB gift link, the link can be redistributed any number of times before someone claims it.
Why do this instead of buying the game from a real store or just send it through Steam is beyond me, but whatever.