Activated charcoal/carbon is standard media for use in all (but, specifically Brita) water filters and chemical respirators. It is literally a sponge that can absorb colour, taste, smell... Toxic chemical in extreme conditions.. but this is really just a very creative way to add an additional level of filtration to the kit wine process. Bentonite clay is similar in kits, I assume... because it is it's main purpose in other uses. These are common tools in medical and safety equipment use for absorption of volatile organic compounds.
If you don't flush a brita water filter adequately you will notice a silver hue to the first few glasses of filtered water. It is used in distilling as well and can impart a silver grey hue to spirits. I can only imagine in a wine it is going to absorb the strongest flavors, and honestly all ferments create percentages of aldehydes, propylene, acetone and these are the things that carbon will 'mop' up creating a 'refined' wine.
I really wish I could get my hands on a FWK. This is just a little extra creativity intended to create a cleaner wine. Any colour introduced by the carbon will settle out over time. I admit it's a brave move, but trust that it wouldn't be included if it would compromise the quality of the wine.
Just something to consider outside of the "WTF.. WHY IS MY WINE BLACK?" perspective