More likely "act of compilation" refers to choosing the particular compiler flags for each source code file. These flags come from the makefiles and/or the environment variables passed to Make. And GNU standard practice for "small supporting files" is to put them under an all-permissive license (see "Information for Maintainers of GNU Software: License Notices for Other Files"). So it appears Canonical is asserting copyright on its CFLAGS and its changes to packages' makefiles.