* You can pickup a one handed weapon with either hand.
* You can have one only in your left hand.
* You can have one only in your right hand.
* You can have one in the left hand and one in the right hand, at the same time.
If that had been the case it would have said "You can use a one-handed weapon
in both/in each hand(s) to deal more damage"
... but it doesn't say that.
It is very possible that they've gotten it wrong though. They might have misinterpreted something, or might just have worded it wrong. It's easy to mix up "a one-handed weapon in both hands" and "a one-handed weapon in two hands" in Norwegian... so I won't be too surprised if it's not what I thought it was. But if we're gonna go strictly by what it says in the text, I'm standing by my original interpretation. I can see where your interpretation is coming from and it's definitely possible that we'll find that it was what they really meant, but for now I'll keep hoping I'm right