probably the original story was that he packed up a few skeps from his apiary at Mynyw with the blessing of Dewi (bees and beekeeping were an important part of David's monastic settlements), and took them back to Ireland with him when he returned to start evangelising over there.
Reading a very interesting book by anthropologist Prof. Alice Roberts at the moment, just at the point when she deals with the fall of Rome which coincided with the rise in Christianity and (this is just simple paraphrasing and condensing a complex evolution) the fact that all the administrators and high status 'civil servants' seeing that their cosy sinecures and palaces were at an end just changed their job titles and thus the foundation of the church in Rome commenced and the building and expansion of the empire just carried on in another guise. Of course miracles and such were a handy tool to keep the great unwashed in awe and later became a compulsory prerequisite of canonisation.
In the early Celtic church (which was a separate entity to Rome but they quickly made moves to take it over) A saint was just a holy person, usually living a very simple solitary life.
