Exactly, datafusion is implied batteries included apache bigdata ecosystem.
Polars is chasing the Python Pandas crowd and uses python syntax, handy if you're already comfortable with ipython.
I think the difference is more that DataFusion is built as a library so you can plug it into the product you're building (e.g. Comet, which plugs it into Spark, or pg_lakehouse, which plugs it into Postgres). Polars could be used that way, but it's also a functional package you can pip install and use as a Pandas alternative right now.