First and foremost, it doesn't mean this will happen. He only speculates it might be possible with a source or sources supporting that Kane might be fit to return in regular season.
The biggest source for rumours are player agents. Both Kane and his agent have utilized media relationships to get their perspectives at varying times out into public domain. When Friedman reported an unnamed Oiler claimed they 'broke' the Flames with the massive playoff win that spun into the Flamers rebuild off season, I would bet money that was Kane. He's cocky confident, big ego, and loves the limelight.
I'd personally guess Seravalli talked with Kane's agent and maybe the player. Might have got a rosy, optimistic picture of the player's recovery. Team wise, Bowman has always had to hedge that they don't know when Kane will be back but can't rule out being back before end of season.
Bottom line is Seravalli has earned his bones as a six year national insider on TSN and as a longstanding newspaper guy who qualifies his information with sources. He's pretty measured and even keel with his reportage. He's built, earned, and trades on his credibility.
Ultimately we'll have to wait and see. This is a significant medical situation from the get go largely driven by the player's decision making.