He did that because the shitheads that follow people like Cult of Dusty were sending PewDiePie's follows death threats, so PewDiePie replaced his list with a single link to K-Pop band BTS as a half joke, half attempt to sic millions of teenage fangirls onto said shitheads.
Before this, PewDiePie also followed plenty of people who are not right wing, including Laci Green, Boogie2988, James Charles, and the aforementioned BTS. It's almost like he was using Twitter to follow interesting people regardless of whether or not he agreed with them, just like everyone else.
Rob