Don't know where you got your card from and whether it was supposed to have a "demo" os. If it came with the board, it's understandable it would just boot to show the board works.
Also don't know if that opi could have other boot rom on it. That should be in the specs.
But you should be easily able to flash what you want on the card and use that. If you want to go more paranoid route, get a fresh card by a known good manufacturer from a trusted store and start from there.