Activity Pane still says the "Submitted on" date but the Preview Application (like you found) or if you present the application as a list (there's a side bar to do this) it will show the "Last Edited" date. ?
I got the same email as well, prob erroneous. I also noticed on the portal it now says "Deadline: Dec 10 2022"... I wonder what it means and why it was added there?