No, the United States was not at war with Germany prior to its declaration of war in 1917. Material support for a belligerent nation (a nation at war) does not equate to being at war with that nation's adversaries. Your brother may feel different about it, but this is certainly not how folks perceived it at the time. In fact, Woodrow Wilson highlighted the fact that he had kept the United States out of the war in his presidential campaign of 1916 (the year after the sinking of the Lusitania), and the Germans for a time ceased the practice of unrestricted submarine warfare in order to keep the United States out of the war. Note also that the United States did draw the ire of the Germans by shipping so much war material to Britain, but this left the Germans in the awkward position of balancing between the sinking of American shipping and keeping the United States out of the war. It is very astute of your brother to make the link between American wartime trade with Britain and its eventual entry into the war on the side of Britain, however.