This question already has an answer here:
This question is currently showing as last edited 2 days ago by "Community", but the last edits are from mid-December. I have enough rep to see deleted entries, so it's not that. This question is not the only time I've seen "mystery bumps"; I think I saw one on the main site on Friday (also "Community") but didn't have time to ask then and now I've lost track of it.
What can cause a post to be bumped without a visible reason?