That is revisionist history. The Confederates became aware that Lincoln had launched a war fleet attack against them, and neutralized the fort before all the fleet could arrive to attack them.
They offered Anderson a truce, but he refused, vowing to fire on them with the cannons of the fort if Lincolns attack fleet engaged them in combat. Beauregard was left with no choice but to prevent getting shot in the back by the Troops in Sumter.