The wording could be a bit confusing.
It means when you are wielding a weapon that is not 2 handed or when you are wielding a versatile weapon in one hand.
If that's the case then it's really poor wording. Like to the point of just being grammatically incorrect.
It is very poorly worded, but it's trying to get across the idea that you can't use a versatile weapon without a shield because, otherwise, it defaults to a two handed condition.
There were folks who had trouble understanding that in early access. They were trying to use a versatile weapon in one hand without a shield, and the game was registering the weapon as being used in two hands, negating the dueling bonus. I suspect the wording change was meant to make it clearer, but it unfortunately added a bit of new confusion.
