Ah, in my research, I did also come across this specific meal being a traditional Swedish meal, which I guess, they chose to emulate:

In Sweden the traditional Swedish meatballs are served with lingonberry jam alongside boiled or mashed potatoes and gravy sauce.

Source: https://en.wikipedia.org/wiki/Vaccinium_vitis-idaea

Could be that IKEA replaces the lingonberries with cranberries in some regions of the world, since they're not too different taste-wise, but I have no idea, if they actually do that.