readme.txt in that directory says:
These textures along with many others are available from:
Many thanks to Nobiax for making these freely available!
However that site says (emphasis mine):
There are people who are able to make games but who are not good at modelling or texturing and they don't necessarely want to pay for it (students & indies). If they are honest & respectful they give me credits and if they want to redistribute (for free) them for specific softwares (UDK, Unity,...) they just ask for it.
The author requires everyone who wants to redistribute his textures ask for his permission first (did Qt get that permission?). Also this paragraph does not explicitly allow modification. This is unacceptable for distros like Debian.