Exactly what it says.
That the ownership or copyright still belongs to whoever owns it in the first place (that is, if anyone owns it).
It makes it clear that Islamic Network does not own any of the audio or text, so to speak. Some audio has actually been provided by audio projects funded by users of the api for use by everyone - but whether they choose to exercise a copyright (if it is registered or even exists in some countries) would be entirely their decision if they see that someone is profiting from it.
I don’t think they would because their motive is not profit - but profit and money can be ugly subjects, so everyone has to make their own decision in this case.