He won't call himself an atheist because it's, in principle, impossible to prove a negative, but "agnostic" on its own might suggest that God's existence was therefore on equal terms of likelihood as his non-existence.
他不愿意把自己称作无神论者 因为原则上是不可能证明一个否定的说法的， 但不可知论者这个说法却可能暗示着上帝的存在 因此跟他的不存在的可能性是一样的。