What was the activity?
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On July 21, a spammer posted a spam link as an answer. It was deleted shortly thereafter, but deleted answers still count as activity on the question. That is why it says there was activity 24 days ago.
Now, activity must come from someone. That spammer's account was destroyed at the same time, so that leaves no one to have performed the last activity. Thus, the system just blames the "Community" user as a default.