These are tags that you have imported from Kubernetes. Hence why it has [Kubernetes] in brackets. You can see more of an explanation here: https://www.dynatrace.com/support/help/technology-support/cloud-platforms/kubernetes/other-deploymen...
The OneAgent will use the Kuberentes REST API to read all the metadata at deployment time. So as long as the service accounts under which the pods are running are given view access (via rolebinding or clusterrolebinding objects) they are able to read labels and annotations and translate them automaticallly intro Dynatrace tags and metadata. Your labels will appear as tags with the [Kubernetes] context, whereas annotations will appear as custom metadata at the Process-level in Dynatrace.
The command you see at the at the bottom of the docs page is a generic one that can be used to give the viewer role to all default service accounts in a namespace. This works in most cases, but it will have to be tailored if non-default service accounts are used for any of the pods.