It's kinda the way that there will always be cats that look 'kinda like' Siamese, Persians, Bombays, Bengals, etc, etc, etc. The breeds were created using domestic cats in their heritage- even the Savannah- so of course, some domestics will look moreso or less like certain breeds. For a Savannah kitten- you want big, tall ears, you want them up-up-up on the head. You want super long legs and a triangular shaped face.
Those are cute kittens, but they don't actually look like Casin- for example. He's not a perfect Savannah- I don't know any that are, but his ears are growing, his legs are getting there, and he looks like a Savannah- not a moggie.