Reading the e-mail it looks more like a fraud prevention action - they want to see the credit card you used to purchase your ticket. Some Asian airlines (like TG) do this all the time. Just do not forget to bring the credit card!
Ah yes, this is likely what it is. This happened to me once before on some obscure Asian airline (I think in Myanmar). Surprised to see it happen on AirBerlin!
I can easily bring my cc. I guess I have to call just in case. Can't have the flight cancelled on me.
Thanks all