I never get Eastern Bluebirds at the feeders during the summer, but they do show up regularly at the feeders during the winter when the supplies of berries become low.
And I guess this is a fairly rare moment to have two males feeding together without any aggression towards the other. The Cornell University's website, All About Birds, says "The Males vying over territories chase each other at high speed, sometimes grappling with their feet, pulling at feathers with their beaks, and hitting with their wings." Pugnacious is another term that the website uses for the males' behavior. Guess I caught them during a quiet interval.