There are similarities and yet differences in that statement. Enough similarities that he can feel that this is Wei Ying. But even more differences that make it hard to comprehend how such things could have been changed.

"So this is Mo Xuangyu."

This body is at least. The soul is clearly different. So the same technique was used but for some reason behaved differently. It's a lot to process. As well as the fact for him it was only 13 years...while he waited for 16 years.