While it sets a shitty precedents to pull a DMCA claim because you don't like the person LPing or streaming your game it's still not cool to casually drop the "N" word during a "heated video game moment". As vile as that word is it makes it all the worst given Pewdiepie's context. Again it's still awful to use merely for "shock humor" just because the word is so "taboo" but it's leagues worse to casually use it like it's just a normal insult.
As for the DMCA claim, yeah I totally get not wanting your game associated with a racist. Though what's to stop future claims from being filed against Youtubers who's politics, religious views, or lifestyles companies disagree with? Yeah the Youtuber could fight it and probably win but lawyers are expensive and I assume all but a handful of Youtubers aren't stinking rich from posting content. Sad thing is Youtube has made it abundantly clear they will only go to the bat for the largest of channels that don't really need their help in the first place. Even if you are one of those large channels Youtube will turn its back on you immediately to appease one of its advertisers.