That all makes sense. J like the idea that Starfleet would trust Picard enough at his word to at least investigate, and it makes sense that a Romulan would get out before any investigation revealed anything.
Also, apparently the Federation media loves to talk to Picard, and he's apparently pretty famous. . .when his ultimatum to Starfleet is to investigate this thoroughly, or he'll tell all to the media. . .and they know he would, and to hell with the consequences.
At this point, with all the things they would have learned that a Starfleet Commodore was a deep-cover Romulan operative, that there's a whole planet of synths, that apparently said Commodore ordered the outright murder of some Synth ambassadors just to conceal this fact, that Maddox was murdered, and such, that Picard having an explanation for it all that makes sense would really help to tie this up.
I was left with the impression that, to the Federation public at large, Picard is seen as something of a hero and celebrity, if Picard says that the Synth rebellion on Mars was the result of Romulan sabotage, then that's good enough for most of the Federation ESPECIALLY if they can get any actual hard evidence to substantiate that.
Starfleet Command may resent him for standing by principles when they were taking a much more realpolitik approach to the Romulan Supernova, or that he is outspoken on that point even a decade and a half later. . .but one thing he's never done is to lie or misrepresent, and they know that (it's rather a key part of his character), and they know that.