Twitch uses audiblemagic to scan all saved VODs of streams for music and mutes anything it finds specifically to prevent streamers from getting DMCAd. Those are not DMCA notices sent by any copyright holder, that is just Twitch's internal system muting anything they think might be music. Lots of streamers then incorrectly end up calling those automutes being "DMCAd" on stream and Twitter.
You can tell by all the screenshots being of Twitch's VOD manager page that shows streamers what got muted. Notices about actual DMCAs on the other hand are only sent to the streamer via email and don't show anywhere on Twitch currently. Lots of people confusing those two including some news orgs.
RIAA and the music industry are hitting Twitch very hard right now with massive waves of takedowns mostly for people just plainly playing music on stream but also the occasional claim for ingame music made specifically for the game or things like people doing outdoor streams and walking by some music playing randomly in the background in a store somewhere but there's also a ton of misinformation being spread by people completely misunderstanding basic things about both how Twitch and copyright law work unfortunately. It's quite a mess.