He literally just temporarily contained it before it fully expanded, redirecting it before it broke the gate, and somehow that action got exaggerated to oblivion
Typical brain rot power scaler argument, where even something as simple as pushing gets exaggerated to the moon.
His body is literally emptied of energy, yet Boros is still conscious after tanking the blast like a chad. The little to no energy left in his weakened body literally made Genos think "And that man would release such an entity into this world?"