Were those pictures taken with 35mm film?
Your initial instincts are correct. I would hazard to guess that most of the better photographers on this forum would never make a 40"x60* enlargement from a 35mm negative unless it was some kind of special circumstance. There is a reason there is a Large format section of the forum and an Ultra Large Format section.
Originally Posted by fastw
My question though is what makes you think he is making those types of enlargements from 35mm film? I am no expert but I thought he used a 24.5+ megapixel DSLR and a 39 megapixel Hasselblad. I'm sure he has plenty of 35mm film images from back in the day but I didn't see any indication that they are available for sale in that size. Is there a particular image in his gallery that you know for certain was taken on 35mm film and is for sale in that size? Like I said I am no expert so someone who is familiar with his work would have to point out the 35mm film images that are for sale.
From what I saw in his gallery I personally don't think his work would benefit from big grain. I'm not a huge fan of grain but it can certainly look good with B&W film.