Im not a copyright agent, but I do know that just because it states commercial/non-commercial, that does not mean you can take that freestuff item {in this case a picture} place that picture in a set of your own and offer it free or for sale.

My backgrounds for instance, I offer for free..commercial/non-commercial..I dont however allow redistribution of that background, by itself, or in a set of someone elses backgrounds. You can use that background in a scene..say for a Poser scene backdrop, and sell or give away that 'render'..as long as you give me credit for having supplied the background.

I have textures that I offer for free also, and you can use them in your 'rendered' images..you cant place them in a set of textures, or give them away separately...

First and foremost, check the providers readme..then if you still are not sure, ask them..if you still get nothing, then assume you 'cant' use the item as you want. 

As for this particular provider, if they have an account with SCG, you can private message them...they do have to come here in order to upload more content...If they dont answer in this forum, or rather dont check this forum, you can always ask around the various large CG sites or do some searches to see where they are a member of....Renderosity would be a good place to start searching ;)