"Hmm.. A slight clarification: If the concept of God is an invention of humanity then any concept attributed to God is also an invention of humanity."
Does not follow. If you have a bunch of things in a bucket and someone takes away the bucket. It does not follow that all those things will automatically fall into the same new bucket.
Consider the question: "Would there be a God if there were no Men?"
The analogy works just fine, because the items in the bucket (concept of human rights) were never ultimately contingent on the bucket (concept of God) but rather on the owner (humanity). It might be accurate to say, however, that the owner did once think that the bucket was required to carry the items. In fact, it may very well even be true that the owner would've never been willing to carry the items without the bucket. It may still be true to an extent.
Someday humanity will grow up. ;)