Kurzik armor on Luxons?

Can someone explain to me why I see Luxon warriors wearing Kurzik armor, and how I would go about doing so? I'm a Luxon and would like to pick up a set of Kurzik armor for my warrior as well.

they played in kurzick territory for a while..

well, You are considerd an ally of the kruzicks(not title related) if you have more Kurzick faction then luxon faction and vica versa.
So have more Luxon faction buy luxon armor, simple as that.
oh and pls use the search button this has been asked a lott before.

Although your guild can only be allied with one side at a time, nothing says that you can't play through both sides in the storyline. A lot of people do both just to see everything in the game.

Whether the merchants and crafters in a Kurzick- or Luxon-aligned outpost will speak to you is based on your current unspent faction. If you have more Kurzick points that you haven't cashed in, then you can deal with the Kurzick NPCs, even if your guild is allied with the Luxons. Because it's based on unspent faction points, and not the total number you've earned, it's easy to go back and forth between the two sides. Be aware that cashing in faction points for one side will cause you to lose faction points from the other side -- though again, this only pertains to unspent points, so all you need to do is make sure that you've cashed in all your unused Kurzick faction before building up Luxon points, and vice versa.