Clearly both Davis & Beauregard believed what they believed, regardless of Lincoln's words.
So there was no actual choice.
DiogenesLamp: "The problem was, the orders sent by the navy for all those men and ships said exactly that."
But Lincoln's final orders, as we have reviewed before, said exactly what he told SC Governor Pickens -- no use of force or reinforcement if no Confederate resistance.
So clearly Jefferson Davis' use of "if you have no doubt" roughly corresponds to RE Lee's use of "if practicable" in his Gettysburg orders to Second Corps commander Ewell about Culp's Hill.
Ewell decided it was not "practicable" and so lost the whole battle for Lee, while Beauregard decided he had no doubt and won the battle which started the war that destroyed the Confederacy.
Such "ifs" were just the way Southern gentlemen addressed each other in those days.
But therein lies the rub. The Confederates had been sieging Ft. Sumter for something like 3 months with the stated position that the Union contingent must leave.
To then back down under the threat of attack is an idea that no one would have accepted at the time. Both sides understood that allowing them to provision Sumter peacefully was not going to happen. Lincoln knew this before he sent the fleet. He was counting on it. They would have actually outsmarted him had they just allowed this to happen.
Given what both sides understood about the situation, the orders were effectively an attack order for the Union fleet to sweep away the Confederates seiging the fort.
The only problem was, the fleet didn't attack as everyone believed it would. Lincoln had used secret orders to send their biggest gunship on a wild goose chase to Florida, all the while hiding from it's sister ships in the Union and Confederate observers who would relay information of it's whereabouts if they identified it.
Clever trick that. He told the Confederates he was going to attack, and then didn't.