Yes there were troops on board. Going to a federal military fort. Imagine that! The ship was nonetheless unarmed, and unable to mount any defense save repelling a boarding party. And Johnny Reb fired first, instigating armed rebellion.
The only thing you’ve been the first to tell me is your incredible nonsense.
The captain of the Star of the West ordered them to remain below deck as they approached the channel because he knew that if the Confederates saw military uniforms it would result in an attack against them. It would be regarded by the defending forces as an invasion.
But what the Captain didn't know is that other ships had spotted the troops and cargo being offloaded from the Brooklyn at sea, and they knew where these troops were going. They got to port and telegraphed the Charleston Authorities.
Anderson seized Sumter in the dead of night with force. The Confederates had trusted the Union troops to be honorable men, but after they had done that, no further trust would be forthcoming.
They also didn't have long to wait for another demonstration that Union officers would lie. Gustavus Fox claimed humanitarian reasons for being allowed to meet with Major Anderson. What he was really doing was involving Anderson in his plan to reinforce the fortress. He was on a military mission, and lying about it. They finally realized that they had been lied to quite a lot when they started opening all the mail between Sumter and Washington DC.