Yup, that's right.
There's many thing that has been predicting about what happen, sometime it's nothing to be happen, such as earth shift or others.
Not all people who make predictions are scientists. There were a bunch of people predicting that the world was going to end in 2000. Of course, the world didn't explode. Those weren't scientists.
The scientists who are talking about the possibility of that asteroid impacting onto Mars give specific numbers for the chance it'll happen and updating the number as they make more observations and discover the asteroid in archives of images and refine the orbit of the asteroid.
Here, there is an animation showing how the asteroid's path and chance for impact had been adjusted when new information comes in.