I generally agree. But, there is more to this story, I’m sure. Domestic violence calls are close to the top of the list of “cop killers.” I’d be especially weary in this situation. I wonder if the woman at the door is the same one who had called the cops a little bit earlier? If so, the cops probably expected her to let them in.
When she doesn’t, and the guy is standing behind her only partially seen, the cops aren’t sure whether she has the freedom to talk openly. He might have a weapon or a realistic threat against her to be exercised when they leave.
Nonetheless, if I were the DA, I would have dismissed the charge before hearing. “Reaching across the threshold” is a bright line.
The article answers some of your questions and uncertainties.