This is a stupid question which people think is the equal to 'can God make a rock so big he himself cannot lift it?' The answer is, because everyone agrees George Washington existed. There is evidence supporting he existed, documents, things he interacted with, family, friends. You can say the same about Jesus and whatnot, but those documents have been altered by the Roman Catholic Church. Why the fuck would anyone fake the life of a person that was not viewed as a prophet sent from heaven? George Washington was a normal person, albeit being the first president and whatnot. No one has any reason to lie if he ever existed.

Does anyone in their right mind say 'George Washington didn't exist?' No. There are hundreds of religions that go against the Bible, but nothing that attempts to refute that he actually existed. What, you think that they actually forged documents, history, brainwashed everyone who has ever seen him, and everyone who says he existed is a liar?

There's your answer, plain and simple. Someone, by your logic, can say 'Does Africa exist? Because if you haven't been there, you're only basing what you know off others'. Honestly now.