I think 'Matty Groves' became a common title because someone 'processed' the original, (as folkies are wont to do), and the shorter name and form was simply easier to say & remember. ('Musgrave' is not a familar name.)

A number of the original names from Child have been altered, or have several names collected from different sources..."Edward" or "Son David", "Sir Lionel" or "Old Bangum", "Lord Thomas & Fair Ellender" or "The Brown Girl", "The Suffolk Miracle" or "Holland Handkerchief" ...etc.

It is good to KNOW the original names and the general history when possible.