I had totally forgotten that! But how do we know that Bo-Katan knows that what she saw is the mythosaur? Perhaps that's a stupid question because she's Mandalorian royalty. I guess I'm asking if she specifically has referenced mythosaurs during the show and if I had missed it.
the mythosaur skull is one of the symbols of Mandalorians, so I'd assume even if she never saw one in the flesh she would recognize it. But even beyond that i think its been shown to have been depicted in art and things like that.