Depending on the situation, there may be a statment from the creator about what you are allowed to do with the files. Commercial uses means any use where you would make money using the files.
If the meshes don’t have any info about that type of thing, then you can’t assume that it’s OK to use the meshes, a lot of stuff is out there that might be ripped from a game illegally.
and even when it says “commercial use license” keep in mind that depending on the website, these meshes (and other content) might be acquired in shady ways.
so if you are doubting about the websites you are downloading from, dont hesitate to ask here or in a variety of ue4/game dev related communities