The title is highly misleading — which should be obvious enough to anybody who has been using Linux in the last 15 years. Of course Linux has been able to use more than 8 cores this entire time. Many of us would have noticed a long time ago if it didn’t
The article is talking about a minor optimization of scheduler granularity to make better use of multi-core machines. It would increase the size of the scheduler’s time slice to make use of the fact that in a highly multi-cored system, you would very likely have some core available to react to user inputs fast, even if processes are running, thereby saving on some context switches. Apparently, this optimization didn’t not go as far as originally planned for CPUs with more than eight cores.
Personally, I don’t expect it would have made a major difference of it had.
The headline here is frankly going past a simplified summary and well into dishonest territory. I would take everything this author says with a huge helping of salt, including his claims that all the documentation and even code comments about that mechanism are wrong.