There are many technical bugs on upwork webapp.
As am a .net based senior developer, i found many bugs on execution of the application. even i faced issues and i update support immediately. suppor on upwork is lightning speed, just post your issues and instant services are provided.
3* will reuied your upwork career, get it resolved immediately.
Of all the weird things that can happen on Upwork, I have never known a "stray" contract and feedback appear on someone's profile so I would suggest you take a close look at your My Jobs > All Contracts page and make sure the "include closed contracts" box is ticked.
Click on the contract and look at all the tabs, messages etc - Chances are it will remind you of the job in question.
On the Terms & Settings tab, you find a link to the original job post, proposal etc, and also a link to see all the contract changes further down.
That will shed light on the matter.