I feel like you’re conflating the orchestration with proxying. There’s no reason they couldn’t be using caddy or traefik or envoy for the proxy (just like k8s ends up using them as an ingress controller), while still using docker.
Docker is the container engine. Swarm is the orchestration, the same as Kubernetes. The concept of "Service" in k8s takes care of a lot of the proxying, while still using Docker (not anymore tho). In Swarm, services exist but only take care of container lifecycle and not traffic. While networking is left to the containers, Swarm services always get in the way, causing issues that will require a proxy.
In k8s for example, you can use Docker and won't need a proxy for ZDD (while you might want one for Ingress and other uses)
