It is the Suphis II of Manetone, brother and successor of the previous one, which more exactly is called in the latercule of Eratosthenes Sensuphis, and Sensaophis. And this is the Chephren of Greek historians, author of the second pyramid.
So, he did refer to Herodotus - the "Greek historian" and proceeded to make the same mistake, not knowing that Khnum Khufu and Khufu are simply his prenomen and throne name respectively.
Have my posts made any sense? Or should I just shut up?