Lyner and Arthur were moving in speeds that no human eye could follow. If a normal person saw them fighting they would only see blurry figures moving around, and confused them for ghost. Lyner knew the moment Arthur attacked that he wasn't going at his top speed. So to be able to match up to the old man's speed Lyner needed to lose some of the things that weighed him down, which were his guns and sword.
Still Lyner was amazed at the way the old man moved, there was no excessive movement at all. He uses the least amount of strength as he attacks. It was obvious from the start that Lyner had an overwhelming advantage in strength, but Arthur made up for that with experience and skill.
While Lyner was being amazed by how an old man like Arthur was able to fight the way he did, Arthur was also amazed by how Lyner was fighting.
