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.
Ell no s'anomenaria ateu, perquè és, en principi, impossible demostrar l'oposat, però agnòstic per si sol podria suggerir que la existència de Déu té per tant la mateixa probabilitat que la no existència.