An officer is checking out something that appears suspicious. An armed man approaches.
Correct. What irks me, is that invasion over something I don't see as reasonably suspicious. OP wouldn't have left it like that either if he thought a reasonable person would have thought so either. That's what leads to the dangerous circumstances.
Did the officer have any way of knowing that the man walking toward her with a firearm was the resident who owned the car? Did the officer have reason to be concerned for her safety until the forearm had been secured? Did the OP think about any of these things?
This can be written, just as easily as:
Did the OP have any way of knowing that the person who was in their yard uninvited was not presenting a danger (fake, malicious LEO) or was in pursuit of a BG who presented a danger to him? Did the OP have reason to be concerned for his safety? Did the officer think about any of these things?
This isn't meant to be argumentative, but this comes from my opinion that the LEO in this case was responsible for creating the dangerous situation, not the OP.