Nope. I have one more theory that doesn't make the cop look like a criminal, nor the homeowner seem like the most naive doctor in the world who can't tell a cop from a pervo/burglar. It all boils down to a detail that some of you have missed. One that is actually quite a coincidence.
From the OP, it sounds like the lady locked the dogs in another room before answering the door.
No, she wasn't answering the door.
OP stated:
after she gets the dogs in some kind of order she goes to the front door and opens it slightly to look out.
So several minutes after hearing a loud noise that sets her alarm off and gets her dogs barking, she finally happens to crack the door just as the officer is walking up. This is a pretty good coincidence.
Now, I also find it hard to believe a cop would walk up to the front door with gun drawn, but when seeing or hearing the door open BEFORE he even got there, he might have drawn in preparation of apprehending a burglar and/or defending himself.
For all we know, he was planning to take off the mask when he got there, knock, gun holstered, and identify himself as the police. But he was startled into a different response.
Then after identifying that the lady was the homeowner, he assumed she already knew who he was. Afterall, from his perspective it would only be natural to assume she had seen him pull up through a window, then come to open the front door for him.
The only part of the theory I'm having trouble with is that he didn't yell "police" when he drew his firearm. Perhaps he had the gun drawn, already. Maybe there have been some armed break-ins in the neighborhood, recently.