Sounds like the PD arrived while there was active shooting inside. It's a possibility that they entered immediately (as they should if they hear gunfire at a home invasion call) and surprised the homeowner before he had a chance to put the gun down.

My instructions to my family is to explicitly provide 911 with my detailed description and to specifically request they relay that info to responding officers. And to also explicitly state that I am armed so please don't shoot me. Not sure what else one could do to avoid this sort of accident/mistake.