No.
Actual situation: cop goes into room, botfried shoots, cop shoots back, accidentally kills Breonna. Cop not guilty; shooting was self defense against boyfriend.
Hypothetical: non-police citizen goes in, gets into argument with boyfriend,say, boyfriend shoots, man shoots back, accidentally kills Breonna. The shooting is still legit self-defense, but now Breonna was killed by a non-police officer.
Does the same law that shielded the cop, above, from liability in killing Breonna also shield the non-cop shooter, below, who also accidentally killed Breonna?
1. Even though we'd like to equate the police officer with the citizen, the officer is sworn by the state, given a badge and a gun. With that power comes certain expectations and certain protections.
2. In the hypothetical with the citizen, if we compare to the Breonna case she is standing next to the shooter as he took a shooting stance. She wasn't sitting on a couch, or in another room hit by a penetrating bullet. If your hypothetical citizen shot back and hit the person standing next to the shooter, that might be viewed differently than hitting someone who is separated from the argument.
If a citizen accidentally discharged a gun in an apartment and it went through wall into another apartment, they would also be charged with reckless endangerment. If they killed someone in the next apartment, it would likely be manslaughter. In your scenario where two citizens shoot at each other and a third-party dies, they would both likely be charged with manslaughter.
-PJ