Yes this is the information that Scott provided in the first Kontakt videos. He said that using a single instance of Kontakt saves on RAM but uses more CPU.
I agree that this is a bit counter intuitive.
What I notice on my 8 core is that I often have 7 cpu cores below 20% and 1 core spiking.
Maybe it is a matter of load balancing the CPU cores by opening separate instances of each plugin.
There is a thread about this on the NI site.
But obviously this makes archiving projects a headache since Logic does not save these sampler instruments and Kontakt has no global sample management on a per project basis.