That "initial commit" was the import of the whole kernel tree into git, ignoring any previous history; that commit having been made by Linus does not mean any particular file was written by Linus.

You should instead look into historical repositories like https://archive.org/details/git-history-of-linux, which go further back; however, before Bitkeeper the authorship of each change was not tracked in detail (that historical repository IIRC does not have the detailed Bitkeeper history, but there is another repository somewhere which has it).