They look like real objects to me, not mockups. Note the subtle imperfections, wrinkles, etc.

A quick Google shows it's the original work of a design student. He probably took real objects (envelopes, etc), transferred his design to them, and then photographed them. Or he photographed blank objects and then added logos in Photoshop.

http://weandthecolor.com/jorgen-grotdal-identity-rebrand/32028