Whether or not it's "written" somewhere doesn't mean that there isn't a stereotype as to how 'holy' men (it's always men...) should behave. Witness the confusion when Westerners got into Indian religions in a big way, then couldn't quite square the way some gurus shagged themselves silly - 'holy' men were 'supposed' to be celibate, if not in actuality, then at least in behaviour. It isn't the done thing to have your Anglican priest bragging about his last shagging session with his wife, for example.

Or is the author using 'reverend' as a joke appellation, without seriously being one?