It's talking about occurrences of the word, not contributions. That's a really lousy way to measure corporate contributions.

IBM is contributing a lot. LWN publishes development statistics after each kernel release: https://lwn.net/Articles/1022414/. IBM was 5th in terms of lines changed, 17th in terms of changesets, 20th in terms of signed-of-by counts. That's alongside the contributions by Red Hat which was higher in all but lines-changed terms.