There was no denying Robin's skill, which certainly must have been developed through practice-- as someone whose primary responsibility was working the knights through their paces and improving his own abilities, Arthur knew exactly the sort of dedication that took. However, there was more than just practice at work here; Robin had a true gift.
One whose depths had not been remotely plumbed, apparently. "Your king is a lucky man, to have such talent in his guard," Arthur declared, shaking his head and letting out a laugh of disbelief at the shattered arrow.