That number is what the error in their calculations would have to be for it to hit the earth. Or in other words, their calculations would have to be more accurate than that in order to know it wouldn't hit the earth. That's a strikingly small error to have to calculate things to. So small that it leaves a lot of doubt that it is calculated that accurately.
These "scientists" are probably a lot like me. They've taken just enough calculus to screw them up for the rest of their lives.....they probably can't even do long division any more...