I usually use "lab" to refer to the opposite of production. My lab is a space where I can change anything at any time and no users are going to be affected. But it seems like this article uses "lab" to mean "my critical services."
Yeah, I guess it's somewhat "half-and-half" currently. The k8s cluster is definitely an experimental zone. The spare cycles on the main ESXi host are also available for testing out ideas, etc. However, I guess a benefit of having regular backups and an easy way to re-provision the services with ansible means that the risk (and cost) of breaking something is fairly low.