"I don't know how it works, so it must be fake news."

To be fair, the person being skeptical is just a surgeon, this is not a peer-reviewed study or anything actually scientific.

Your NPR link even shows that scientists realize there are still unknowns:

> "We think that nail stem cells may a have a special function to induce the whole regeneration process, including nerve attraction and growth of the bone," Ito say.

A cursory search seems to say that typical regrowth of a nail takes 4-6 months, but Spievak claimed his only took 4 weeks.

Can we say definitively that his "pixie dust" had nothing to do with it? I don't think so. Can we say it did have something to do with it? Also unknown... but the answer right now IMO certainly isn't a scientific "no."