Is not feelings that Axel was talking about, it was the fact that Sora still had his sense of self, and memories, which all lose once they turn into Heartless. The only other man to ever do that was Xehanort.
Who else had his sense of self? "Ansem".
The story here is:
And it doesn't matter if Ansem The Wise found Xehanort without memories (that was ten years ago), because this all happened when they were experimenting and studying the heart (later on when Xehanort became Ansem's apprentice), which, obviously, turned fatal. Xehanort was too involved in figuring about the heart (in other words, obsessed), Ansem figured it was too dangerous and forbid Xehanort to keep studying the mysteries of the heart, he disobeyed, got the other assistants, who were also too involved (first 5 members of Org. XIII, excluding Xemnas) into his side, and lost their hearts, etc. You know the split that happens after.
Their Nobodies, including Xehanort's, were the beginning 6. And, the
13th Order originated.
Sora killed Xehanort's Heartless already. And by KH2, his Nobody.
Also, Commit it to memory is the literal translation of Axel's catchphase in Japanese. I guess since it was that catchy, they changed it to Got it Memorized.
No, "Got it memorized?" is more better and more of a literal translation, as the Japanese version pose more of a question than a statement.