You don't need to be an expert to write working software. You don't even need to be an expert to write good software - you do need to be knowledgeable in that field to write maintainable software, but even experts in the field often write bad software in the name of expedience.

Yes it was more a joke about the terrible quality of code produced by physics. Obviously they write stuff that works for some bizarre value of 'works'. Of course this being HN everyone took it super seriously ;)