I've seen the BA Prem, QF Chairman, AY Plat, EXP and Concierge Key luggage tags before and its fairly clear which they are with visible text/airline logos etc. What I saw was literally plain matt black with nothing but the emerald logo, and I did check it out twice. Best guess is it was the light and the new Prem card.

Incidentally can be useful now to have luggage tags with the new boarding procedures. I don't have them but my GF does and when we were boarding and having the yellow tags put on, the gate lady issuing tags said "oh you are Gold, that's OK" and moved on to the next pax. Not sure if it meant anything, but there you go.