Intel is the top documented contributor to the overall kernel (as opposed to the "core" of the kernel, which is defined here has non-driver, non-architecture dependent code) with 11.4%, whereas Oracle has 2.2%.
7.7% are attributed to "unknown", 5.5% as "none", and 2.4% as "consultant". Almost 2/3 of that combined quantity would need to be attributed to Oracle in order to make up the gap, which seems unlikely.
So the definition of "core" seems to be the key factor here. Intel, AMD, IBM, Huawei, Linaro and Red Hat contribute substantial amounts of architecture-dependent code and/or driver code which isn't counted in this metric.
> Could it be that some Oracle employed contributors are using a different email when submitting pull requests?
Yes, and if you contribute from an e-mail address that Greg K-H's scripts don't understand, you get an e-mail from him asking you to disclose your employer if you're willing.
Some companies mandate you contribute from your corporate address, and it is impossible to contribute from some corporate e-mail accounts, since they don't allow SMTP access for use with git send-email. For example, my understanding is that this is the reason for the linux.ibm.com subdomain, though someone at IBM can probably elaborate.
LWN's numbers are probably pretty close to accurate, as I think most people disclose. I haven't read TFA, but I guess Oracle is counting only commits to kernel/+fs/+net/ or something like that.
Could it be that some Oracle employed contributors are using a different email when submitting pull requests?