No, it's not a ghost update because it happened not in GCKey but in the tracker
I just noticed that my review of medical results in GCKey was updated from May 9 to May 10 on either September 6 or 7, which might be the reason for the hidden update in the tracker. But based on my search on this forum, it's common practice for the IRCC to add 1 day to the medical exam date, yet nobody has reported a hidden update in their tracker after that. So I guess these are two separate events. And idk what to except