Interacting between Host and Kubernetes Cluster Network for Mosquitto MQTT

Cluster information:

Kubernetes version: v1.28.3
Cloud being used: no
Installation method: kubeadm
Host OS: Ubuntu 22.04
CNI and version: calico
CRI and version: docker 24.0.5

I have set up a Kubernetes cluster on my host machine and deployed a container within the cluster. To test communication, I used kubectl exec to run the mosquitto_sub command inside the container. Simultaneously, on the host machine, I executed mosquitto_pub. I successfully received the message inside the container.

My understanding is that the host and cluster networks are distinct. Could someone explain how this communication is possible? I’m curious about the network intricacies that allow messages sent from the host to be received within the cluster.