Robin's bow was actually a Longbow; not the bow he uses in the show. A Longbow is, of course, long (about as long as the person using it) and is virtually straight. Also Robin never used the Saracen sword and the movement for a long sword are completely different meaning he actually wouldn't have been able to.
They use several words that were not known at the time this series took place (1192). Both "illegal" and "cancer" were used in the first series. According to Merriam-Webster the term illegal was first known to be used in 1538 and the term cancer was not known to be used until the 14th century.