I am quoting it in the exact context in which you presented it and the new portion cited does not change the context.

Relevant portion of your post verbatim:

"To the President of the United States, Washington D.C., January 1, 1861. From the Commissioners from South Carolina

"You received and acted on assurances from the highest official authorities of South Carolina that no attempt would be made to disturb your possession of the forts and property of the United States if you would not disturb their existing condition until commissioners had been sent and the attempt to negotiate had failed. You took from the members of the House of Representatives a written memorandum that no such attempt should be made, "provided that no re-enforcements shall be sent into those forts, and their relative military status shall remain as at present."....Scarcely had their commissioners left, than Major Anderson waged war. No other words will describe his action. It was not a peaceful change from one fort to another; it was a hostile act in the highest sense- one only justified in the presence of a superior enemy, and imminent peril. He abandoned his position, spiked his guns, burned his gun carriages, made preparations for the destruction of his post, and withdrew, under cover of the night, to a safer position. This was war.

No man could have believed (without your assurance) that any officer could have taken such a step, "not only without orders, but against orders." What the State did was in simple self-defense; for this act, with all its attending circumstances, was as much war as firing a volley; and war being thus begun..."

I don't see that my statement is out of context at all. The subtext of all of the commission's claptrap about "meaning no harm" is "as long as you give us exactly what we demand" and "how dare you move before we could seized you." South Carolina was playing false the whole time. They were not negotiating for reunion or anything other than complete recognition and acquiescence by the U.S. government to their claimed secession.

As for a threat by Anderson, his comment is a private discussion with his superior, not an official or public statement to the South Carolina authorities. He is not threatening South Carolina because his statements weren't being made to South Carolina, unless they were being passed on and were perceived as such by the South Carolina government. If that was the case, one must then ask how or why his comments within his department to his superior would have reached the ears of a force regarded by the United States government as rebels. Considering that Cooper, the recipient of this message, resigned his commission in March of 1861 and became Adjudant and Inspector General of the CSA, perhaps it shouldn't be too surprising.