In A Separate Peace, why does Gene say that peace has returned to Devon?

The novel begins at Devon during the Summer Session of
1942 when Gene and Finny, along with the other members of their class, live lives that
have not, as yet, been caught up in World War II. During that summer, the boys discuss
the war, but it seems very far away from them:

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The class above, seniors, draft-bait,
practically soldiers, rushed ahead of us toward the war. They were caught up in
accelerated courses and first-aid programs and a physical hardening regimen . . . We
were still calmly, numbly reading Virgil and playing tag in the river . . .
.

This summer represents the
last moments of peace in the boys' lives for many months. When the fall term begins,
with its regular classes and regimented schedule, Gene says, "Peace had deserted
Devon."

Throughout the following chapters, the war becomes
ever-present in the boys' minds as it moves closer to Devon--and to them. Leper enlists,
which makes the war a painful reality to all but Finny, who refuses to acknowledge its
existence. Seemingly immune to dreary weather and the general depression among the boys,
Finny plans and executes a raucous  Winter Carnival, complete with
cider.

During the festivities, Gene performs amazing and
silly physical feats, behaving completely out of character, and it is at this time that
for a short while Gene feels that peace has returned to
Devon:

It
wasn't the cider which made me surpass myself, it was this liberation we had torn from
the gray encroachments of 1943, the escape we had concocted, this afternoon of
momentary, illusory, special and separate
peace.

During the Winter
Carnival, the boys are free to be school boys, as they had been during the Summer
Session. The world is at war, but for a little while they again feel far removed from
it. It is only a momentary peace, however; Leper's telegram arrives, shattering the
illusion, bringing the reality of World War II back into
their lives.