The Netherlands has one official capital, Amsterdam, but the government is in The Hague. I reckon the other countries in the quiz have some similar situation.
The Hague is the Seat of Government (all 3 branches) of the Netherlands but is never considered the Capital. The only Capital is Amsterdam (this is constitutional).
No. Your thinking of the capitals of the 4 constituent countries that make it up. That would be like saying that every state capital is a capital to the main country of the USA in addition to Washington DC