User blog comment:LoveWaffle/First details about the MCU's Ultron emerge!/@comment-8284722-20140718030629/@comment-1895174-20140718061542

Didn't the Hydra guys in The Winter Soldier's mid-credits scene refer to the twins as test subjects? And the description Whedon provides is that of characters who recently got their powers. All evidence points to they're the results of Hydra trying to create their own super-powered team and not that they're mutants.