As larrabee said, it's all done electronically, so his biometrics will be linked to his application number in the computer system... so I believe the stamped sheet was just to inform New York that biometrics had been attended before mailing the passport.
However, the visa itself will be processed in Sheffield, with the online application form, biometrics and all the documents transmitted to the Sheffield offices electronically. Then once it has been processed, Sheffield will inform New York of the decision, then New York will issue the visa vignette into his passport and mail it back to him.