Admittedly similar reasoning never stopped Christian rulers calling themselves Caesar.
But that was with the precedent of Constantine and his successors, all the theology they built up around them, and the verse where Christ supposedly endorses the rule of someone named "Caesar" by saying "Give to Caesar what is Caesar's." There're no similar precedents for a ruler named "Pharaoh."
That being said, I like the scenario proposed upthread where some Crusaders simply think "Pharaoh" is the natural title for a King of Egypt. It's less likely due to Exodus (hey, where was the precedent for a "Defender of the Holy Sepulcher" or "King of Jerusalem"?), but I think it could happen.