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.
Nenazval by se ateistou, protože je v principu nemožné dokázat neexistenci, ale pouhé slovo agnostik by naznačovalo, že existence Boha je tím pádem na stejné úrovni pravděpodobnosti jako jeho neexistence.