I don't claim. I write according to what scholarship says. If you don't understand the problem, it's because there is no problem.  Both comments above are pointless except to underline an unfamiliarity with the distinction between ancient texts and secondary scholarship. Let me illustrate by using your claim of a contradiction and restating what I said re Moses, as if it dealt with Odysseus, another fictional person.
'Odysseus is a fictional character invented by Homer and Homer's Odyssey is not a source for explaining the etymology of the name.'
No one would blink at that, except . . .
Just as 'Moses/mashah' is a kind of figura etymologica used by the writers to explain a name whose origins they did not know, so too is 'Odysseus/odussamemos'(Ὀδυσεὺς/ὀδυσσάμενος at Od.xix.406ff.).  This is very frequent in ancient literature. Just as modern scholarship doesn't accept the  Biblical etymology for Moses, so classical scholarship has generally disabused itself of the idea, stated by Autolykos, that Odysseus be named  'child of hate/woe' because his grandfather was in wrathful odds with the world.
γαμβρὸς ἐμὸς θυγάτηρ τε, τίθεσθ᾽ ὄνομ᾽ ὅττι κεν εἴπω: 
πολλοῖσιν γὰρ ἐγώ γε  τόδ᾽ ἱκάνω,
ἀνδράσιν ἠδὲ γυναιξὶν ἀνὰ χθόνα πουλυβότειραν:
τῷ δ᾽  ὄνομ᾽ ἔστω ἐπώνυμον:

The ancient Jewish readers of the Bible were quite aware, as we can see from Philo of Alexandria and Josephus, who both proposed an Egyptian etymology. In doing so, they dismissed the folk etymology given in the Tanakh, realizing that that the derivation from the verb 'to draw from' was an infra-Hebrew folk etymology, a kind of Figura etymologica as ancient rhetoric classified such games, that had no value. How could an Egyptian-speaking princess in 1,500 BC be sufficiently fluent in a language that was only attested in that form several hundred years alter, to give Moses a name that would make sense a millennium later? In medieval times, once direct and living contact with antiquity was lost, all sorts of fantastic speculations developed.