a) The female cult walled city fell recently, killed by them trying to kill someone who was infected who then turned into a monster and killed them all.
b) The female cult walled city fell recently, killed by a rival group who they antagonized somehow. Still possible that one of them was mortally wounded and turned into a monster killing both groups.
c) Female cult fell years ago, it's a trick so he could steal their stuff.
d) There never was a female cult, this is just some random fortification and fallen settlement that he drove past once and it's a trick to steal their stuff.