To be fair if this is the case, they only way this would be a mistake, is if its automated.
Which if it is automated, then by that logic it should detect the smash soundtracks and get rid of them.
it is automated
which is why fan smash remixes got taken down before smash's release when the ost was leaked, even though they weren't real, the bots mistake them for the real deal just because they're labelled with smash
It's also why, despite the bots ruthlessly targeting the three houses ost, TH ost vids disguised as memes get through, cause the bots don't realize that they're real
who knows why they're taking down the Splatoon ost, but it's certainly not smash related, like I said, the bots don't care about smash
Consider that there are Splatoon ost vids on that channel with songs that are
actually in smash which haven't been taken down. It's either a mistake, or simply the beginning of another purge on this poor dude's Splatoon vids (the last time they were taken down was when he leaked the smash ost, which got a bunch of his other vids taken down as well, including the Splatoon 2 ost)
Now, if the bots were actually going after smash right now it'd be different, but this dude has over a hundred smash vids which are still up and haven't been targeted since the game's release