What does the behavior of Starkfield's citizens imply about New Englanders' attitudes toward outsiders in Ethan Frome?

Your question is a complicated one, because you ask both
about behaviors (of which there are few) and the citizens of Starkfield, who are
stereotypical, close-mouthed New Englanders.  These two factors in Ethan
Frome make it difficult to determine how much of their reticence to speak of
either Zeena or Ethan is protectiveness and how much is simply their natural
disinclination to be talkative.

Clearly the narrator is a
newcomer in town, here to do a temporary engineering job.  At the post office, he gets a
bit of Ethan's story.   He learns that the only mail they generally get is the newspaper
or mysterious packages from odd patent medicine companies.  He learns there has been a
"smash-up" which has left Ethan not only incredibly scarred from head to toe but has
also left him looking like "a man who was dead and in hell  now."  He learns that Fromes
live a long time (perhaps even if they shouldn't or when they don't particularly want
to).  He learns that Ethan had to stay in Starkfield to be a caretaker--first for his
father, then his mother, and now his wife.  The town native, Harmon Gow,
says:

“Guess
he's been in Starkfield too many winters. Most of the smart ones get
away.” 

That's a good start
on Ethan's story. The narrator's landlady adds a few more details: Ruth Varnum saw them
first, it was a tragic event, and it happened down at the bend of Corbury Road.  After
that, no more.  The narrator said:

readability="10">

on the subject of Ethan Frome I found her
unexpectedly reticent. There was no hint of disapproval in her reserve; I merely felt in
her an insurmountable reluctance to speak of him or his affairs, a low “Yes, I knew them
both…it was awful…” seeming to be the utmost concession that her distress could make to
my curiosity.

That's actually
quite a lot of information from this very tight-lipped community.  Harmon Gow is clearly
sympathetic to Ethan's plight, and the landlady appears to be unwilling to speak any
more of Ethan's woes.  If she's protecting anyone, it's Ethan.  It appears more, though,
that the episode (the "smash-up") simply makes her inexpressibly
sad. 

I'm gathering you haven't read beyond chapter one, so
I want to be careful about how much I reveal here; but it seems that any reluctance
Harmon has to speak of the event comes from his natural disinclination not to speak too
much to strangers, and the landlady's hesitancy to speak comes from her unwillingness to
talk about painful subjects. Neither appears to simply distrust foreigners and refuse to
talk to our narrator.