However, as I understand it, the rebus-like hiero (priestly) glyphs (pictograms) were deciphered by men who knew the vulgar (public) language of ancient Egypt, demotic (demos=the people in Greek). This was the key that unlocked the language because hieroglyphics were essentially symbols that when read showed them to be pictorial demotic.
While this is not Srednik’s area of expertise, he tries to be well read in language studies.
That’s why the Rosetta Stone was so revealing.
It had Greek, Demotic, and Hieroglyphics with the same message.
I remember my Dad walking into the British Museum and seeing the Rosetta Stone. He let out a gasp. He had read about it so many times, and THERE it was.