Did you disable the default_indexers as well?
According to the documentation, this processors has two building blocks, indexers and matchers, so I'm assuming you need to disable both as mentioned in the documentation.
This behaviour can be disabled by disabling default indexers and matchers in the configuration:
processors:
- add_kubernetes_metadata:
default_indexers.enabled: false
default_matchers.enabled: false
See if changing this solves your issue, if not, please upgrade to a supported version and check if the issue is still happening.
It may be a bug, this version is 3 years old.