I hope this is the right place...

There is a shop inside of Schiphol Departures called "Dutch Food Gifts" that has a lot of specialty items, lots of cheese. It also happened to be the most convenient place for me to buy a Coke. So I grab a Coke, went to the front, handed the register woman the Coke, grabbed my 2.50 euros, then she asked to see my boarding pass. She then proceeded to ask me my nationality then asked me for the 2.50 euros.

It was early, I hadn't slept the night before, so I complied with all requests. What happened here? Was I unknowingly used for some corporate data collection? Or is a lot of their stuff duty free, meaning I was just a victim of formality?

https://www.schiphol.nl/en/page/airport-maps/
Departures > #41 darker blue (next to the casino)