When I traced the navigation using the "Back button" and the link, I observed a difference in the tracer:
1) If user selects the link to go back to the previous step, then the activity "pzUnsubscribeFromPush" is called after which GoToPreviousTask activity is called. 2) If user navigates using the "Back button" then the GoToPreviousTask activity is called directly.
Are you looking for a JS way to detect Back button click versus link click?
Beyond the Pega Support forum, if you look at other web forums, there are multiple solutions being discussed including one way to detect back button click specifically using the mouseevents ClientX/ClientY coordinates. Thanks.