Quote - ... was specifically referring to the god of the Old Testament, so whatever the Egyptians had going on isn't even relevant to this part of the discussion.

Only kind of. The principle generalises to all notions of a god or gods.

People have always used god(s) as placeholders for things they are otherwise unable to fully explain, comprehend, or control; hence even the earliest gods were anthropomorphic. Only later did anthropotheism appear, followed by theomorphism.
The zoomorphic gods of the Egyptian and other similar early cultures are what became the basis for demons and devils in later ones.