What makes me curious is that (as best as my PhD in Organic Chemistry from Google, with advanced studies at the Wikipedia Institute for Trivia Studies can tell) the various calcium-phosphorus-sometimes-other-stuff compounds that you'd find in bone aren't particularly black; but the article specifically mentions that outgassing was absolutely unacceptable (because of the sensitivity of the instruments) so they must have done a fair bit of scrubbing of the chaotic mix of oxidized organics that you'd find in bone char to arrive at the spacecraft coating compound; but I don't know what you would leave in to arrive at something that is both charcoal black in color and calcium phosphate in composition.
Probably just another item on the 'things I don't know' list; but it's much more puzzling than if they had, say, gone with carbon black, where you'd plausibly assume that they'd scrubbed out everything but the carbon dust and called it a day.
Pigment aside, this surface bonding treatment sounds very interesting indeed. The oxide layers on aluminum are stubborn things, so the idea of getting your choice of surface property baked in is intriguing. I wonder if I could improvise with a sand blaster and a supply of welding gasses in my back yard?