1st of all, he really is that knowledgeable and great, props to oro for knowing so much.
2nd thing is, its weird that through all this time he didn't do this and recovered his arms before? I kno' he was trying to get sasukes body, but even with it he would still need his DRS hands :[
Kinda off topic, but no wonder people wanted to destroy uzumaki clan, this kind of seal/unsealing powers that we'r actually now seeing for real are that amazing and powerful after all