I got an answer to my question from the Ollama community on Discord.

"localhost" means two different things inside vs. outside of the docker container. Open-webui sees locahost as local to the conainter. My laptop sees localhost as local to the laptop (which does not include the container).

So not all localhosts are equal. Now I need to figure out how to expose a virtual interface on the laptop that is accessible to the docker container, but not accessible from other hosts on the physical LAN.

It sounds like I need to learn more about how to manipulate the docker.internal network.