The original Robin of Locksley (the Robin Hood of Pyle's stories) was a minor noble, and all nobles in England at the time (of the setting, not necessarily of the "historical Robin Hood" whose very existence is questionable but was seemingly centuries later) had at least some French Norman blood.
French was spoken at court. Much of what became "high etiquette" was based on French court customs, and the well-known English disdain for the French and anything pertaining to them stems from this period of what some see as "foreign rule".
In short, Robin Hood most likely was French in the stories, though Pyle never seems to have mentioned it (nobility being French was simply expected and needed no explanation).