Is 1 Corinthians 5:11 applied to only people who call themselves Christian or all people that believe in Jesus as Christ even if they don't call themselves Christians?

11 But now I am writing to you that you must not associate with anyone who claims to be a brother or sister[a] but is sexually immoral or greedy, an idolater or slanderer, a drunkard or swindler. Do not even eat with such people. (NIV)