Mortensen does a ton of these interviews and likely has some idea about the questions that will be asked. He also likely has numerous sources (some of them might even be sports agents) that he can get information from to use in his report(s) and interview(s). I'm also starting with the premise that it is in Mortensen's best interests to stay on top of potential candidates for NFL openings.
do I think that Mortensen just pulled those thoughts out of thin air? No. Do I think Kelly (via his agent) has let it be known that he would be open to an opportunity away from ND? Probably. Do I think that Mortensen might have heard it and then checked back with the agent and/or the agent might have reached out to Mortensen to see if there might be any NFL interest for his client? Likely.