Find out "Giveaway-Creator"

if the giveaway was public, open the link in a logged out browser/tab and you will see it.

btw, you can see the avatar and name of the person in your wins page. http://www.steamgifts.com/user/p3monty/giveaways/won

visiting your own profile while not logged in might work as wel. I can see your group and invite only Wins as well (with creator)

edit, just see that Mullins edited her comment to add it as well ^^

Ok, thx a lot both of you :)