He's giving information about things that will be answered in KH3, just like Xemnas in KH1. I'm definitely not going to trust the opinions of KH fans on what they think the connection is between the ES's words and KH3.

-He notices Sora because of the Keyblade.
Well, he is one of the current wielders of the Keyblade, along with Riku and Mickey (I will not include Kairi). I think that ES was probably a wielder of the Keyblade in the past around the time when Xehanort was still alive.

-He says he's met Sora before.
Only KH3 can answer this.

-Then says "No...it isn't you. It isn't you that I have chosen..."
Again, KH3 can only answer this.

-Repeats the word "Xehanort" a couple times. (Possibly mistaking Sora for Xehanort?)
All that I can conclude is that Sora and Xehanort are connected somehow. KH3 will probably fully explain it.