The difference is that a general purpose database typically organises data by fixed-size pages, so new data could be anywhere in the file as there is no guarantee of page ordering with regard to inserts. Whereas a specialised file format for logging would add new records at the end of the file (or in a circular fashion, depending on the design). But will have features similar to a database like a defined schema, and some form of indexing. This is true of systemd journals and Windows event logs anyway.