[Non-Sequitur]

There was no reason other than mobilization for warfare against South Carolina for Anderson to remove himself from Moultrie to Sumter.

Actually there was. Anderson moved his forces in the face of threats from the South Carolina mob to storm and seize Moultrie. Moultrie was indefensible from the landward side and Anderson was, quite rightly, concerned with the safety of the men under his command.

[Maelstrom]

There was no threat to the men under his command so long as he was not preparing for war against South Carolina.

There was no batter way to establish exactly his intentions than to remove himself to Fort Sumter creating a choke point in the harbor.