I see that you are deep in the details there! I imagine that your “googled” source is telling you the density of wood, which is made up of mostly cellulose. The cellulose that is in the THERM library is a type of insulation like cotton, which is also made mostly of cellulose (but importantly has a lot of air spaces in between the cellulose fibers).
Needless to say, simply referring to a material by its chemical makeup is probably not the best practice. The material in the THERM library should probably just be called “Cotton” and the material in google should be “Wood.”