Judging by the placement, I would say it's aftermarket. The cold drink switch is inside the arm rest (at least in my '08 335i e90). And all that does it route a little A/C to keep it cool.
Then again, it's possible that at the time of your build, BMW hadn't put the switch in the armrest yet. This could be one of the first models with the cooler, and the switch was placed there as a "quick fix".
2008 Monaco Blue/Tan interior 335i sedan. Mods: AFE intake w/ scoops, AFE Exhaust, ER FMIC, Koni FSD/Eibcach Pro-Kit, Breyton Race GTS wheels w/ Continental ExtremeContact DW tires, Cusco OS strut bar. BavAuto Black/Beige seat covers w/ black floor mats, M3 rep trunk lip, eBay front splitters.