iirc they put basically every death that happened under socialists countries, even natural causes such as old age that you mentioned, and diseases, and boy oh boy, 100 years of colonization, rural and illiterate china did have a lot of diseases, a lot of people was dying from easily preventable or diseases that were eradicate in capitalist center.

and as you mentioned, people that never existed in the first place, used a wacky population growth chart for china, that didn't come to reality, so they counted this as victims too.