Our anger about what qualifies one as a manufacturer of a tobacco product is misdirected when we aim it at the FDA. It needs to be aimed at Congress. They are the ones that put into law the Family Smoking Prevention and Tobacco Control Act (in 2009) where they defined manufacturer. (see below) The FDA is simply following to the letter of the law the directive they were give. (I underlined the word assembles).
"(20) Tobacco product manufacturer.-- The term 'tobacco product manufacturer' means any person, including any repacker or relabeler, who--
"(A) manufactures, fabricates, assembles, processes, or labels a tobacco product; or
"(B) imports a finished tobacco product for sale or distribution in the United States.