Heard from whom/where? Whatever, it’s hogwash, containerization is bigger than ever, and Docker is seen as synonymous with containers (there are others, rarely used). Kubernetes (aka “k8s”) is a platform for orchestrating and deploying containers, much like Docker Swarm. You’d use Kubernetes when you need multiple containers working together (aka “orchestration”) like, let’s say a database container, a webserver container, and a redis container. Kubernetes lets you define your different containers as one logical group, have them share a filesystem, connect to each other over a private virtual network, and start/stop them all with one command. If one of them goes down, you can automatically restart it, and your web traffic gets a spike, you can have it spin up more webservers automatically.
My shop is all cloud-based and going 100% containerized, and we don’t have any plans to use Kubernetes. It’s really made to manage single organizations, whereas we have several clients with no relation to each other whatsoever. Doesn’t help that k8s on AWS isn’t free, whereas ECS is.