Apparently the term "bomb cyclone" has been round since the 1940s among meteorologists.
Only in the last few years have they used it with the general public to scare us and enhance ratings.
Bomb
Popular expression of a rapid intensification of a cyclone (low pressure) with surface pressure expected to fall by at least 24 millibars in 24 hour.
But Atmospheric River isn’t listed
https://forecast.weather.gov/glossary.php