It's likely to be DLC - Diamond-like Carbon coating and the coating looks to be black which I would think is the obvious indication that a coating has been applied, it's not a permanent application as it still wears through but it takes longer for the part to wear after the coating has been applied, from what I can gather there's not a great deal to gain performance wise but it stops the mechanical parts wearing prematurely and keeps the gap sensitive valve train/gear measurements in mechanically safe tolerance for much longer than stock parts which would defo help in a high rpm race spec motor. No idea why it was banned but it doesn't appear to be a cheap process or another possibility is that they've found some health issues in the manufacturing or handling process.