HAOS runs on a real machine or a VM
Container runs in Docker on a real machine or VM
HAOS lets you add containers that it manages
You have to manage them yourself if you use the HA container image.
I use Docker and run HA as a container in it. It works but much of the documentation assumes (or appears to) you are running HAOS. It is mostly the same, but the differences are frustrating until you understand that they exist (backup for instance).