If we open source code for action started from controller find-threads (XF\Pub\Controller\FindThreads:actionStarted()), we can see ability to set user id who threads is interested for us. And when we set this user id, in UI we continue see tab "Your threads" as active.
Thank you for reporting this issue, it has now been resolved. We are aiming to include any changes that have been made in a future XF release (2.2.0 Beta 2).
Change log:
When viewing "Threads started by X" page only mark the "Your threads" tab active if you're viewing your own threads.