Verified answer

You are referring to the "magical, tissue regenerating pixie dust" that has been in the media again recently - re-growing the guy's finger.

Sadly, this isn't a genuine finding (apparently the lab re-releases this information to s different set of journalists every time they need new funding).

It was only the tip of the finger that was severed - and the guy's nailbed was still intact - so it is entirely unsurprising that his finger-tip re-grew.

Read the linked article for a good debunking of this sensationalist story.