What is a "primitive container" vs. a "non-primitive container" in Kubernetes C Client API?

I am exploring the Kubernetes C API. When analyzing the data types involved, I see that the v1_pod_dns_config_t contains three attributes of type list_t. The comments state that two components are “primitive containers” and the other a “nonprimitive container.” However, in a unit test like the one in test_v1_pod_dns_config.c, all three of the lists are constructed with an ordinary list_createList(), so it is difficult to discern how they differ. I try searching for “primitives,” and the only place I find it is in this documentation page.

I must be missing something obvious. Can anybody help me understand it? Is it simply stating that the nameservers and searches will be string types, and the options will be of a more complex (struct) type?