You are using both with your energy generated numbers. That's where they come from.
Your solar TWh comes from 25GW at ~15% capacity factor, and to get your nuclear numbers you're looking at 1.6GW for each of nuclear "plants" when each reactor is usually about 1GW or less. There are ~90 reactors in the US, at 54 plants. The article is assuming 1 reactor per plant for the Netherlands.
