He’s categorically denied over and over again that he’s interested in forcing Biden into a primary and I think it’s a misread to see this as anything more than a governor doing their job. He’s never left any ambiguity in his answers on this topic.
A politician’s denials don’t mean much.
He can easily say that the the polls are showing that most Americans seeing Biden as mentally and physically unfit for President and would even vote for Trump, so he is reluctantly stepping up to save the country from Trump.
It’s also very common for inside knowledge on an exploratory committee to be leaked to the press ahead of a run. Serious candidates hire a team to strategize months before making an announcement and it never stays silent because the exploratory committee itself tends to leak in order to gauge the early reaction. We’ve seen neither of these things from Newsom.
Besides, there is no political way that, should the position become vacant, Biden would choose a white man to replace Harris.