I was about 15 at the time and live quite close to Ballyroan at the time, there was many stories the one that stick's out the most was that the family where part of a religious cult which was total nonsense.
As far as I recall it was based on the fact that his mother went to Mass everyday or was part of a prayer group (like hundreds of other women of her age, but why let that get in the way of spreading some scandal).