It is really not surprising that an Episcopal school - there are several of them in Austin - has sold out to a fully secular agenda. Who would stop them? Certainly not the Episcopal 'leadership'.
Episcopal schools are just secular schools that charge tuition.
I've heard Austin is pretty liberal. I could imagine this occurring in an Episcopal school not far from here -- but in, say, the Diocese of San Joaquin it would be more difficult to image. (I could be wrong.)