When editing an article there is an "Update" checkbox in the editor. If you don't tick that box, the date is not changed and the article is not marked as updated (and shown again on the main page page).
You probably forgot to check that box and Sean has not edited your article (I guess he is shown as last editor because he approved the article so that it does not need 5 user approvals).
At first, I clicked "Update article" (at upper-right corner of the page).
During making changes I periodically clicked "save draft" button (beneath the article).
At last, I checked "I have read and agree ..." and finally pressed "Publish".
Latest update was related to code changes.
I think it was essential improvement of my code.
You know that but a reader would not. If you have a history section as already suggested old readers will know immediately what has changed and new readers will see that you work on it. From my point of view that is much more important than a precise date on top (the history will then contain the exact date).
There was an editor note on your article that said "I just removed one empty line" so I didn't mark the post as updated. Looking at the revision history I can see there were a lot of changes. I have now marked it as updated.