I just can't find any evidence to suggest that Argonians "descended from Ehlnofey" so I'm going to continue to assume that their origin is more alien. Also, the evidence we do have suggests that the Argonians are tied closely to the Hist (i.e., they can sicken from being cut off from the Hist, licking the Hist is part of the passage into advlthood, etc.).
So, at the moment I prefer theories that assume the Hist created/changed the Argonians and that they did not come from the Ehlnofey.
"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."
While that could be interpreted as inconclusive (though so could the Khajiit idea, really), I think it makes it pretty likely the Argonians evolved from the Ehlnofey.