I honestly don't know, but probably not that uncommon as naming for the father has carried into the modern era. No less confusing to have three generations of John Smith.

The eldest getting a given name may have been a status thing, perhaps tied in with succession. Eldest being the one that would inherit the land or title. The young had all sorts of opportunities to die, and even escaping childhood was no guarantee as you'd then be expected to make up a Lord or King's retinue of men for any conflict. Maybe it's the origin of popes and some monarchs taking a name on succession - the "job name".