Talk freely about the scene, the world of remixing, or anything off-topic unsuitable for the "Fun Forum".
As long as it's not an instance of someone claiming to be the creator of somebody else's work, I would consider this particular situation as an instance of free promotion. It's always a possibility that somebody who potentially like your music could come to discover it by that very YouTube video alone. This person also liked your music enough to give it a listen in the first place and even feature it in a gameplay recording, which I would personally find appreciative. Let's not undermine the fact that the uploader was also respectful enough to give credit. That way, if a listener were to stop by and actually catch interest in the music, they do have a clue about what to look for. Otherwise, I suppose viewers can always ask in the comment section if they care to know.