They are atomic scientists, so they actually aren't even experts in any of those fields. The risk of nuclear war is a geopolitical question which has nothing to do with the science behind the weapons.
Quite to the contrary, the clock is set by the Science and Security Board which seems much more focused on geopolitical questions instead of scientific. The Science and Security Board is advised by the Board of Sponsors, which does have quite a few scientists, but only in an advisory role.
"Atomic scientist" isn't even really a thing. This is a political advocacy magazine, and always has been.