The bombs fell because the girl fell. Artificial gravity is within the bomber. She fell from the top of the bomber shaft to the bottom of it just like the bombs did. And once the bombs hit the vacuum of space there’s nothing to stop them from continuing their trajectory.
Except that it’s not nearly enough space for the bombs to reach terminal velocity or even the speed we do seem them dropping at outside of the ship. The top bombs would also have a higher exit speed than the ones below them that stop accelerating the second they enter space, causing the top ones to hit the below ones and possibly triggering a chain reaction explosion (since they’re already armed before launching), destroying the bomber instead of the target…or they push the ones below them sideways in various directions, causing them to go off target and potentially into friendly craft.
So without an actual launch system it’s an incredibly bad and dangerous design to be literally “dropping” bombs in space.