No, an attic is not a concealed space.
There are two threads of compliance that you need to look at. To make it easy, first look at what the manufacturer has listed for the proper use of the material. Most kraft backed insulation has the wording stamped right on the backing "do not leave exposed". The code wording is similar, if it doesn't meet flame spread/smoke index it has to be in substantial contact with finish material (wall board). Whether it is in an attic, a basement or anywhere else it may not be left exposed (exposed to the AIR). Does that help?
R302.10.1 Insulation. Insulation materials, including facings, such as vapor retarders and vapor-permeable membranes installed within floor-ceiling assemblies, roof-ceiling assemblies, wall assemblies, crawl spaces and attics shall have a flame spread index not to exceed 25 with an accompanying smoke-developed index not to exceed 450 when tested in accordance with ASTM E 84 or UL 723.
Exceptions:1. When such materials are installed in concealed spaces, the flame spread index and smoke-developed index limitations do not apply to the facings, provided that the facing is installed in substantial contact with the unexposed surface of the ceiling, floor or wall finish.