From UESP (http://www.uesp.net/wiki/Lore:Ehlnofey):
The progenitors of the Aldmer and various human races. The diverse people of Tamriel become the Mer (Elves): The Dwemer (Deep Ones), the Chimer (Changed Ones), the Bosmer (Green or Forest Ones), and the Altmer (Elder or High Ones). The fracturing of the Aldmer along cultural and racial lines is the Sundering of Aldmeris, and the continent no longer exists. The other Ehlnofey became the beasts, and the humans of Nirn, who will eventually split into racial groups, including the Nedes, Nords, Tamriellic Aboriginals, as well as the Redguards of Yokuda, and the Tsaesci of Akavir.
So since Tsaesci descend from the same Ehlnofey that humans and mer do, it would be weird if they looked like that. And, how can you imagine that kind of snake to rule Tamriel for a few hundred years? I think that Tsaesci might be much more human-like than we think, and them being snakes is just metaphoric or something
EDIT: But, actually, that depiction of Tsaesci could easily be mataphoric as well... So I don't know. Anyway, this game is most likely not about Tsaesci, it's about the dragons. So I think it's not one of them