It really was a blunder with the confidential document; Joo Jin-woo raised the issue

Rep. Joo Jin-woo of the People Power Party posted on Facebook under the title "A serious matter of undermining the state: Why is Lee Jae-myung receiving reports on the NEC special prosecutor situation," claiming, "The part at the end of the document that reads 'NEC special prosecutor, recount of ballots in the Olympic Park Handball Gymnasium [redacted]' appears to have been cut off. They were caught due to a mistake."
Rep. Joo pressured them, stating, "This is strong direct evidence of collusion or surveillance regarding the NEC special prosecutor," and added, "This is a clear crime and a violation of the Constitution that breaks the political neutrality of the NEC special prosecutor. Disclose the entire document immediately."
[Source] - Kookmin Ilbo
[Original Link] - https://www.kmib.co.kr/article/view**?arcid=9000018554