Nyet, King Arthur/Artoria is the one in the blue saber outfit or the male one who has been in hiding for a good while now it seems. The bunnysuit one is The Lion King ^_^ (My personal opinion, at least)
It's a little more complicated than this but the short explanation is
since Lostbelt 6 is a world where Excalibur was never created, there consequently cannot be a King Arthur, because 'the king who has Excalibur' is kind of central to BEING King Arthur.
Even shorter: Artoria Caster just happens to look like what Lostbelt King Arthur would have looked like.
That's my (likely flawed) understanding of it, anyway.