I guess probably because more often than not we see spiders predating other things but not often the other way around, not often observed.

I have to say I don't know a whole lot about spiders, I actually didn't recognise any of the ones in its nest, from what I can tell online they seem to prefer the spiders that live in the long grass around, there's none of the typical common Australian spiders in the nest like whitetails or redbacks or hunstsmen.

Yea I would have to assume it's to do with the mud around, it is fairly clayey(is that a word? lol) around here, some of them do have a more brown appearance so it could be that this one is quite old and has faded in the sunlight.