Warning: Nowhere in this article did they describe the composition of this steel as not containing carbon. The headline is terribly misleading.
Yeah, it appears that they meant "steel produced without carbon emissions", not literally "steel that doesn't contain any carbon", which is by definition impossible.
Yeah seriously. That was my first thought, wondering if an analogous element had been used or if similar crystal structures had been achieved in some other way. I'm guessing some automated A/B test found that this particular headline was really successful due to that confusion.