This is the 4339th most frequent Japanese word.
勘違い
A misunderstanding or misconception.
In this sentence, 勘違い is used to indicate a 'misunderstanding' or a 'wrong assumption' made by the subject.
彼は私を嫌っていると勘違いしていた。
He misunderstood and thought that he disliked me.
Here, 勘違い is used to represent 'a mistake in perception or assumption', specifically regarding time.
彼女は時間を勘違いして、会議に遅れてしまった。
She mistook the time and ended up being late for the meeting.
In this case, 勘違い is illustrating 'a misinterpretation' of someone's intent or statement.