I don't normally defend OMM but I read that article and saw that it was low hanging fruit for a classic DO beatdown so I'll bite this time.
I've heard of this stuff happening in olds, but in a 28yo healthy male for "stretching"? Bit of artistic license in this story...the gentleman in question hyperrotated his cervical vertebrae. Look in a netter book and see how far you need to rotate for healthy normal vertebrae to interact with the artery...The technique taught to students goes slightly beyond a point of tissue restriction within the normal range of motion and immediately stops regardless of whether a 'crack' is heard, but never to the point of hyperrotation.
Now whether this technique is safe? Maybe in experts' hands, but I wouldn't trust a student or senior resident with my neck because most can't recite from memory how much of normal cervical range of motion is due to c1 on c2. Nor would I ever use this technique in practice because a more serious concern would be a cervical osteophyte that leads to vb insufficiency. But in a 28 year old dude? Bit of a stretch.