Two possible scenarios, same result: In many cases, when politicians, who are rumored to want Biden to step down, are confronted with this publicly, they deny it. We have seen this happen, not just with Jeffries, but also somewhat with Pelosi, and others.
I am willing to believe these unsourced stories could be trial balloons to take the temperature of the base. Which would mean, these folks got a shit ton of pushback from us, and changed course ( which is good!). I know this happened with my congressman... congressman Nadler. He initially seemed to support the anti-Biden wing, but when confronted in public after a day or so, he recanted.
Another thought I had was this: what would stop some Republican assholes from lying to a reporter and planting scurrilous stories in the press, given the utter laziness and terrible job these stenographers often do. This would not be so bad, if we had a rapid response team who could immediately debunk and call out these lies, but our party ( with notable exceptions) have always sucked at messaging, if not rallying unequivocally around our candidate.