
Swordmanship - Someone who only uses Swords, is part of a School or Style.
Like Zoro said, not everyone with a Sword is a Swordsman. People who are willing to win in any way outside of Swordsmanship is not a Swordsman. Their martial art is like Sanji - he will use Legs to fight even if it kills him.... Swordsmen will always rely on Swordsmanship.
King admits he's not a Swordsman, and I'm guessing Roger, Rocks and many other Blade wielding people aren't Swordsmen.
Vista was said to be the strongest Swordsman in the WBP, most likely because he's the highest ranked Swordsman - he'd still lose to Whitebeard since WB isn't a Swordsman.