Senera's comments were followed by these words in parentheses from the author of the piece, Stephen Rodrick: "An educated guess is she's talking about Sharapova, who is now dating Grigor Dimitrov, one of Serena's rumored exes."
Maria's low blow comments bring to mind "You're So Vain" is a song written and performed by Carly Simon. The song is a critical profile of a self-absorbed individual; Simon asserts "You're so vain, you probably think this song is about you." The subject's identity has long been a matter of speculation - just like the article.
Maria to Serena: Don't get personal