Did he take her with the express intent of her being his wife? Yes. Did his family(witnesses) know that was his intent? Yes. Was it ordained by God from the way she was found? I think arguably yes.

Did he just randomly sleep with a woman and she suddenly had rights as a wife? No, that’s not what happened. It was predetermined and agreed upon what was happening. And Isaac couldn’t forsake his commitment to her because there were witnesses to it.

See the difference?