I don't know why some atheists are always to eager to say that this or that person was an atheist. Saying that you hold the same opinions as someone bright doesn't make you bright.
In my opinion, many atheists are practicing hypocrites, since they get their children baptized, and they marry in a Church. So, saying "that this or that person was an atheist" might just ameliorate the feeling of being a hypocrite? In other words, associating oneself with an accomplished person, that also professes atheism, might make one feel that that justifies one's hypocrisy? "Justify" might not be the correct word/thought, but I think you know what I mean, being an intelligent atheist!