The "Ruins" motif is present in several songs, including Ruins (obvs), Waterfall, Quiet Water, NGAHHH!!/Spear of Justice, But The Earth Refused To Die / Battle Against A True Hero, Don't Give Up, An Ending, and Respite. It's just a recurring leitmotif; it doesn't mean that one song is a remix of the other. Also, Spear has a lot more to it than just the Ruins motif. I once saw a video about all the motifs in Undertale, and it concluded that the Ruins motif is the theme of the monsters of the Underground. Take a look back at my list of all the songs with the motif. Each one is somehow tied to monsterkind (their first home, all of their wishes, the hero/last hope of the underground, all the monsters coming together, and endings of the game)