Hard to tell. It could have been a stress crack from a catch where it didn't come all the way off the chuck. It could be ring shake where the wood cracks along the growth rings rather than off the pith, and it opened up as it dried. I don't see any chuck marks on the tenon, so that may not be the problem. If you return it, I would put some thin CA glue in the crack, then some thick or medium on top of that, and then stand it on edge so the glue will soak all the way down in, let it stand over night, and then make sure to stand out of the line of fire when doing the second turning. Keep the speed down too, not more than 500 or so.
What kind of wood? Black locust?
robo hippy