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.
Il ne se qualifiera pas d'athée car il est théoriquement impossible de prouver une négation mais le terme agnostique lui-même pourrait suggérer que l'existence de Dieu est aussi probable que sa non-existence.