If you just loaded after an update sometimes the icons need to reload, and I think that's the default one that is shown when the icon hasn't loaded yet.
People do that pretty often in trading cities, such as Lion's Arch, Ascalon, and Droknar's Forge. They want you to buy. The under construction, IMO, is there simply because NCSoft hasn't finished the skins for those items.
Probably not an intentional scam (unless he was taking advantage of the current situation somehow). I've noticed in the past that item icons change to that 'under construction' sign a lot during updates which was frequent last night. He may have intended to randomly sell you something valid, but the items showed up in the trade window as our friendly construction guy instead. Turning him down (it WAS a random open trade) was probably the best idea...
ah that's a factions item.. I have a withering focus item for a ritualist from back when the strongbox was around- it has that icon in inventory but the skins finished
here's a pic of the offhand- same under construction icon as posted above