It's been a very long time since they parted, and their time together was limited so while Xingchen realizes the voice is familiar, it's a bit harder to place it right away. The mention of Emperors Smile seems to confirm there's a link to their worlds. Should he have use of his eyes, it would be an instant realization, but the white cloth over his eyes is a reminder that seeing is impossible.

By the time he actually reaches the voice, Xingchen's able to place it.

"Childe Wei?"

But he should confirm his theory first.