Eugene already had a bad feeling the moment his dad didn't reply to him. When Ivan kept informing him what happened inside that dark room, and how it seemed like the people inside were arguing, he couldn't thank Arthur enough for stepping on the gas and going past the speed limit where police or CCTV couldn't spot them
He knew it wasn't right, but a desperate situation required desperate measures. The moment the unchanged black gate appeared in his line of sight, Eugene jumped off the car before the car even stopped.
It proved to be the right decision because he witnessed the door start to close in front of his eyes. He had to jump through the panicking betas and probably shoved some of them aside to reach the door and push it back against his brother.
And perhaps it was the effect of seeing that mug that gave him enough strength to overpower the older guy. Eugene barged in with the sheer power of spite and almost three decades of resentment.
