Yeah, I'm not a lawyer, let alone a UK lawyer, but this seems insane. Why not sue Amazon, Walmart, and Best Buy for selling games that use their music, too, while they're at it. The license to use their music is, presumably, licensed by the game creator. And, if it's not, you go after them, not the storefront that's selling the game, right?

If this case holds water, then didn't that mean storefronts are liable for validating the licenses of all assets used by all products they stock? That would be insane. ("Prove you own the copyright to your packaging, design, layout, copy, music, textures, models, SFX, .......")