First of all, I am not a lawyer. I can not provide you legal advise. This is just how I as a legal layman would interpret this license and what consequences I would make based on that interpretation.
When you have a question about the details of a creative common license which are not covered by the laypeople synopsis, then it can be useful to look at the actual license text.
It defines non-commercial as:
NonCommercial means not primarily intended for or directed towards commercial advantage or monetary compensation. For purposes of this Public License, the exchange of the Licensed Material for other material subject to Copyright and Similar Rights by digital file-sharing or similar means is NonCommercial provided there is no payment of monetary compensation in connection with the exchange.
So yes, using it in a freely available game which does not aim to make any money whatsoever does not seem to be an issue for the creator, at least according to this clause.
OK, but what about the no-derivatives part? Is a game which uses the music a derivative work? The license says:
The Licensor hereby grants You [the rights] to produce and reproduce, but not Share, Adapted Material
Or in other words, you can "adapt" it for your own use, but then you can not give your "adaptation" to others.
OK, but how does it define "Adapted Material"?
Adapted Material means material subject to Copyright and Similar Rights that is derived from or based upon the Licensed Material and in which the Licensed Material is translated, altered, arranged, transformed, or otherwise modified in a manner requiring permission under the Copyright and Similar Rights held by the Licensor. For purposes of this Public License, where the Licensed Material is a musical work, performance, or sound recording, Adapted Material is always produced where the Licensed Material is synched in timed relation with a moving image.
And here it gets tricky. "synched in timed relation with a moving image" appears to talk about using the song in a video. But it might just as well fulfill the definition of using it in a game.
So it appears to me that using a CC-ND license song in a game might not be possible without permission. So you might want to either seek the creators permission to use the song in your game or look for a different one.
By the way, my favorite site for finding background music for game jam games is filmmusic.io. Almost everything on there is CC-BY. Which basically means "do whatever you want, just give credit".
