Mungo (Saint Kentigern) was proclaimed a saint by early Christians long before the official canonization process was instituted in the 11th century. He was probably declared a saint by a local bishop sometime early in the 7th century.
I have placed a link to the biography of St. Mungo below so that you can determine for yourself why he was accorded the honor of saint.
Saint Kentigern, also known as St. Mungo, is the patron saint of Glasgow, Scotland, and salmon.
Saint Kentigern (Mungo) died on January 13, 603, in Glasgow, Scotland of natural causes.
Saint Kentigern (Mungo) was born about the year 518 at Culross, Fife, Scotland.
Saint Kentigern (Mungo) died on January 13, 603, in Glasgow, Scotland of natural causes.
St. Mungo was not killed, he died a natural death.
St Mungo's Academy was created in 1858.
St. Mungo was born about 518 at Culross, Fife, Scotland. He spent much of his life evangelizing Scotland, especially in the area of modern Glasgow. You might say he is a patron because he was a "homeboy."
The city of Glasgow was founded in the year 500. The church was founded by Saint Kentigern.
St. Mungo on January 13, 603, in Glasgow, Scotland of natural causes.
St. Mungo, also known as St. Kentigern, is said to be buried at the Glasgow Cathedral in Scotland. The cathedral, also known as St. Mungo's Cathedral, is dedicated to him and is believed to be his final resting place.
St. Mungo was ~85 years old at his death in the year ~603.