Well that's blunt. Everything about this line says distance, from the passive form of "there's been," to the mention of the death as an objective event, to the phrase "opposite house." This death has happened to someone else, somewhere else. Our speaker's interested, but only as a nosy neighbor would be.
I know it, by the numb look Such Houses have — alway — (3-4)
You wouldn't think houses would have expressions that give away what happens within them, but the speaker says he knows about the death from one numb look. It's to be understood that "Such Houses" are a class of house with which this speaker has some considerable experience. You mean the ones where someone lies dead inside? Yep, those houses. They "alway" have that numb look.
A Window opens like a Pod — Abrupt — mechanically — (7-8)
Let's see if we get this right. There's a window that opens like a pod. Okay, but then it's described as abrupt and mechanical. If you were thinking of a seed pod, you might want to think again. It sounds more like a space pod latch or some other piece of machinery. Maybe this ambiguity—a plant form acting like a machine—is deliberate on Dickinson's part. Maybe it's to suggest a kind of automatism within nature's order?
The Minister — goes stiffly in — As if the House were His — (13-14)
The minister is just one of the many people who go in and out of this house on this death day. Here Dickinson puns on the word "stiff" to play with the notion of the corpse. The minister enters like a corpse, "As if the House were His." And while Dickinson goes on to explain how bossy he gets, acting like he owns everybody, where does a stiff go? There's also a suggestion that the house here is being compared to a coffin. That's not Dickinson being original. Lots of other poets have made that association, think of William Cullen Bryant's "narrow house" in "Thanatopsis."
[…] and the Man Of the Appalling Trade — To take the measure of the House — (17-19)
If the house is a container for a life, the final house is the coffin. Here the undertaker's undertaking is to take the measure of the corpse and the doorways, to make sure the final passage is possible.