How did Mungo Bonham become a Saint?

I just added a bit of historical background to the character entry for Mungo Bonham. It turns out that there was a real St. Mungo who was an early Bishop of Scotland (also called St. Kentigern) who evangelized pagans c. 600 in the Glasgow area. One local tradition even holds that he baptised a bard named Merlin.
According to Jo, the founder of St. Mungo’s was a wizard named Mungo Bonham (1560 – 1659). Neither Jo’s site nor the Wizard card give us much information on Bonham. I now find myself wondering how a wizard becomes a saint!

By the way, thank you to Potter blogger Muggle Matters for posting about this.