Apparently Bob McKenzie said the same thing about Marner on Sunday night:
https://www.hockeyfeed.com/nhl-news/...to-free-agency
It tends to be rare for insiders to report something as definitively as dissentower this far from free agency, unless the player makes the statement. They're all probably hearing the same thing from Toronto team guys that Marner is going to test free agency (but they still want him!), but then when they call the agent he is probably telling reporters that Marner would still like to re-sign with the team and only will test free agency if they can't work something out.
In this case, it certainly sounds like Toronto team guys are leaking this info whether just idle chatter or intentionally to put pressure on Marner's agent to accept whatever offer is on the table.