Lots of ways this could have ended without a dead person:
Identify correct floor;
Identify correct apartment;
Assuming those fail, and you (incorrectly) assess your apartment has been broken into, call for help.;
Realize you need help because you are exhausted and not in any condition to confront a burglar. (In the meantime, maybe realize #1 and #2 were not done);
This is pretty horrible. I also heard of a similar type of situation - armed civilian at home, hears someone breaking into his house, kicking and breaking down the door. He prepares himself and shoots when the violator gets through. But, shit, it was the FD, and they'd come to the wrong house when answering a fire call.
They tell you in CCL training that you better be EXTREMELY sure about what is happening if you're going to pull the trigger, ever. They even encourage not intervening in other people's misfortune because you can't know what's happening - maybe a "kidnapping" is parents trying to get their runaway child in the car and back home, and you end up pulling a gun on the mother, and now the father just sees some dick holding a gun to his wife, and that escalates badly. Observe, call police, unless you and those in your immediate care are in peril.
As for this particular situation... Smells like third degree murder. Seems a little like drunk driving deaths. I think drunks behind the wheel should be held to a 3rd degree murder charge too. That they "didn't mean to end a life" is not a viable excuse for their extraordinary negligence, to me. The same applies here.