It's actually kinda backwards. I think he's probably ambidextrous, as there's one picture where he holds his sword left handed, but the rest it's shown in some way that it's to be wielded in his right. Crono, on the other hand, is a devoted lefty, as even his pose in-game reflects that.
I'm also suspecting that Toriyama is left-handed, as people tend to draw their characters proficient with the same hand as themselves. If you look at Marle, she holds her bow much like someone left-handed would hold a rifle, though in-game she does it right handed. It's all kinda weird, but I just usually tick with what I think would work. If whoever happens to use his right hand in a picture, so be it, as long as the picture is good.
