True. But what if the object that they're connected to is moving? What's to say that ISS wasn't rotating in such a way as to create force?
Now ISS has various gyroscopes and thrusters to keep it oriented. However, it appears that many of the ISS systems were turned off and/or damaged, which means that those thrusters or gyroscopes may not have been working. So ISS may have also had some spin to it, considering that it and the Soyuz had been hit by debris.
So it's quite possible that ISS was rotating or spinning in some manner. While the ropes stopped their momentum, they were still taut afterwards so that implies that there was some force acting on them.