I have often seen, on the front page, a question from years ago showing up as “Active” due to an update made by “Community ♦”. Specifically, this question does not show any activity with ?lastactivity
(accessible from the front page by clicking the link that looks like “24m ago”).
The revision histories of the question and both answers show nothing indicating an edit.
I don't know why it shows up in the “Active” section if the changes made are silent.