> five well-known celebrities (Justin Bieber, Ellen DeGeneres, Kim Kardashian, Barack Obama, and Mark Zuckerberg)

It feels weird to me to bundle a tech CEO and a former President of the United States in with a pop idol, a talk show host, and a reality TV influencer as "celebrities".

Why? They're all undeniably celebrities, and I guess the point was to have a spread of source of celebrity?

Why not? They are all celebrities. Celebrity status is not really correlated to the actual work they do [although some work requires some notoriety]. Gordon Ramsey's a restaurant owner and chef but he's also been on reality TV. Malala became internationally famous for being the target of an assassination plot, not her years of advocacy for women's education beforehand.