When I clicked on the Revisions, instead of the revision, I saw this:
[Edit removed during grace period]
I've never seen this before. What does it mean?
The user made an edit, then before five minutes (the "grace period") passed reverted it (but not via the "rollback" feature). In general if you do multiple edits within the five minutes window they only count as one. If the net result is that nothing changed, there's no difference to show in the revisions window, but the system still records the fact that there was an edit.