If it was "the florist" then where's the proof it was actually Beyoncé.
Like, I can send flowers to myself and write "Love Beyoncé". Any writer could do that to gain status on social media
Why would a seasoned New York Times writer cook up a story like that? Risk career and reputation for what? A moment of social media shine that will be immediately forgotten? Ok.
My first thought was that the handwriting didn't match... But I don't think that means it's fake. As noted, it's common for people to order things and have them written by other people.