That was probably true of the original trajectory, but now it's supposed to fly quite close to Ceres and scientists want updated data to see if a collision is likely.

“Quite close” is relative, given how ridiculously vast space is. The chances that they fire blindly out into space and just happen to hit Ceres seems so unlikely as to be basically impossible.

True, but it's not like you have to hit an object head on, but merely pass within it's gravitational field which is far bigger.

Pass within its gravitational field at a slow enough relative speed for capture. Remains exceeeeeeedingly unlikely.

Nonetheless people are asking SpaceX for data to calculate the probability because they seem to think it's higher than 0 because of the unplanned trajectory.

The pale blue dot image gives some sense of scale here. Is it in the orbital plane of Ceres? I too would be interested in seeing the data results. If it's not orbiting on same plane then risks of collision drops further it would seem - would involve a plane intersection at the exact distance from sun Ceres orbit is at same time Ceres is there.

It will not cross Ceres orbit.