> I'm not sure who started this whole container is just a process thing, but it's not a good analogy. Quite a lot of things you spin up containers for have multiple processes (databases, web servers, etc).

It came from how Docker works, when you start a new container it runs a single process in the container, as defined in the Dockerfile.

It's a simplification of what containers are capable of and how they do what they do, but that simplification is how it got popular.