Yes, currently it uses a SQLite3 DB for storage. The DB is created or updated with Djangos migrate command which runs when the Docker container starts. The DB file can be found in the data folder.
Thanks for your comment, it made me realize I stopped thinking about persistence at some point and now I had to look up on SQLite usage in production. However for the apps current use-case of handling one account / one person it seems fine to use SQLite.