Not exactly sure how I read this. Obviously, Obama is no political dummy, he's as devious as Stalin and Hitler, for instance. But to be blunt, Alexandria ¡Ocasio!-Cortez has already won the Democrat primary in a district that runs 80% Democrat, at least, not including the votes of illegals and dead people. In that case, there is no reason to endorse her as she can essentially do nothing but fly around the country and stump with other commie-pinkos (which, pragmatically, is her ONLY worth; politically, she's a typical leftist lightweight).
Obviously, Obama knows that being overtly socialist is a death wish. Remember "If you like ___ you can keep ___" and "The 80's are calling your Russian conspiracy theories back" were necessary lies to fool the fencesitters. Had Obama been truthful about Obamacare's disastrous results it wouldn't have even passed all the Democrats in the Senate, let alone Republicans who fell for the ruse. So I'm guessing Obama is not too thrilled at some socialist seniorita yahoos in the party throwing out the early tells on the actual Democrat objective, which is to ultimately kill/execute all conservatives. Pure and simple.