Apples versus truckload of oranges. The Chelyabinsk meteor was an apple. It is true that nobody saw it coming. The largest intact piece would have destroyed a building, but not caused a catastrophe. The meteorite was 20m.
The newly discovered object is 400m. Its orbit cannot easily change since it is being tracked and interactions with other objects can be calculated. Even if it hit a unknown 20m meteor like the Chelyabinsk meteor, the path won't change much and can be easily reanalyzed.
The orbit doesn’t have to change.
It’s the orbital calculations that might change.