Did you actually put the mouse cursor over the armor to make sure it stated it was an enigma after you traded?
I'm guessing you didn't; you most likely fell for a trade window switch- do you remember him putting up the enigma, and then saying he doesnt have enough room, then coming back and throwing the armor up fast, trying to hurry the trade? This is why you need to make sure items and their stats are exactly what you want before you click your trade agreement button. The fact that the armor you currently have only has two sockets proves this since an enigma needs three.
Sometimes people will even have 2 ebotdz; one thats low and one thats high; and will trick you into trading godlies for the low one by switching them at the last minute; I'd suggest you go read the scam list stickied in the newcomer forum so this type of thing doesn't happen to you again.
Darnoc