What does spin mean in this context?

This line:
docker-compose --env-file example.env -f docker-compose-triton-gpu.yml up

But these have: different task ids, same endpoints (from looking through the tabs)
So I am not sure why they are here and why not somewhere else

You can safely ignore them for the time being 🙂

but is it true that I can have multiple models on the same docker instance with different endpoints?

Yes! this is exactly the idea (and again I'm not sure what's going on with the actual containers you have spinned , it seems they are not actually picking the configuration and that they server zero models?!)