An atheist believes that an entire category, or type, of thing(s) does not exist (in this case God/deity) . A theist (someone who DOES believe in a god in one form or another) is someone who DOES believe that category of thing(s) does in fact exist. This is a huge separation. It would be like someone saying “We are both A-Universists (Someone who does not believe in the existence of the universe). I just happen to believe in one less universe than you.” It’s an entire category that one person accepts and one denies. The attempt is to create an illusion of closeness in position, when the fact of the matter is that the theist and atheists are on completely opposite sides of this issue.