> Don't get me wrong, I think MS SQL Server is a highly capable DB, I just don't see enough of a value add here to justify the price tag, in general.

I suspect it uses what was called MSDE (MS SQL desktop engine), which is free to use and redistribute on Windows. It is essentially headless SQL Server with most high-end features stripped out and resource governor enabled. With all those limitations it is still very capable (probably too capable for the use case) database.