I think he can get away with it because it's still questionable how much Xehanort actually remembers. I get the impression that he figured out that he was Player, but he may not have had ALL of Player's memories. Maybe he was only able to remember bits and pieces in his dreams.
The "precious light" sounds like it could be referring to the "true dandelion" to me now. More specifically, the light in Ventus. But it's very confusing to hear him talk about it this way. You've already got the light right there, Xehanort! ...Unless he thought that another keyblade war would bring about another light, which would be Sora, I guess? We'll have to look at those lines again in the future because I feel like they aren't going to hold up perfectly.
I get the feeling that there's going to be some kind of big twist involving the first keyblade war. Personally, I have my fingers crossed for more Agito XIIi references. But there really is a lot that we don't know about it... It's essentially the MoM's past. So maybe that's what Xehanort really wanted to know about; what were the circumstances of the very first keyblade war??