No, he doesn't need to take all the supporting docs, just his passport and biometrics confirmation sheet. In the US the biometrics is just a 5-10 minute appointment where they take his photo and fingerprints and it's done by US immigration on behalf of the UK consulate in NYC, so they will have no need to see his other docs.
The reason for the website saying he does need to take them is that the online application form is for people applying in other countries, not just the US and in some countries you do your biometrics at the consulate at the same time as submitting all your supporting documents (in the US, you mail the docs separately).