When you check Settings > Storage you will see the SD card. If it is portable you will see an eject symbol to the right of it. That means you can eject it and use in in another phone/computer etc.
If you don’t have that then the SD card is encrypted and you will not be able to use it elsewhere, so if the phone gets corrupt, and maybe you do a factory reset you will all data stored on the SD card.
How did you get the music on the card? If it was on there before you inserted it into to the phone then the SD card is ‘portable’ i.e externally formatted.
If you place a new SD card in the phone you will have been asked if you want to format it as internal or external. As the top option is internal - Google’s preference many people opt for that.