Weird english

[Nestama]

Y'shtola: "This aether... It was a Crystal of Light." "She, too, was one of Hydaelyn's chosen..."

Is this the line you're on about? If so, then it kinda makes sense for Y'shtola to be vague (though the implication is leaning heavily to WoL), especially as I don't think she had ever met the Elezen in person. The Scions have never seen/experienced a Warrior of Light or someone with the Echo or Crystal of Light perish, after all.