This "Altmeri formwwar", does it refer to the war between Auri-el and Lorkhan? Before the creatures, mer and men gained their static forms?
I'd be surprised if the Sload were part of that war, and it does say "first of the formwars". I'd say it might be contempraneous with that crazy period, and the time of the "forest people" mentioned in Words of Clan Mother Ahnissi, when divinities walked the earth.
I thought that according to the altmer that Minotaur's and an now extinct bird man like race ruled over tamriel? o.O
Never heard of minotaurs ruling Tamriel, but bird men come from http://www.imperial-library.info/obbooks/father_niben.shtml, and it never says they ruled there, nor is it necessarily talking about the same era as the OP's quote. Also, Father of the Niben has several anachronisms anyway that makes it dubious. Not to mention that birds and minotaurs would have a hard time ruling "slave oceans"...
Um.