Oh, you're familiar. Yeah--don't get too starstruck, he was pretty full of himself.

[An understatement. But Waver looked thoughtful for a moment, then continued.]

It's a 'collective unconscious' sort of thing when it comes to Servants; recorded human history influences a fair bit about them even if the core legend remains generally true to life. So I guess you could say it's a matter of memory, sure.