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은 아니었다

was not

→ 은
phrase Rare #22,191
was not 은 marks the preceding noun or phrase as the topic and can add contrast.
KO: 그건 내 선택은 아니었다.
EN: That wasn't my choice.

부자가 될 만큼은 아니었다.

It wasn't enough to make me rich.

내 탓은 아니었다.

It wasn't my fault.